LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 


GIFT    OF 


Class 


UNIVERSITY    OF    CALIFORNIA 


DEPARTMENT  OF  EDUCATION 

Gift  of 


Received 


LESSONS 


IN 


CHEMISTEY. 


BY 

WILLIAM  H.  GREENE,  M.D., 

EMERITUS  PROFESSOR  OF  CHEMISTRY  IN  THE  PHILADELPHIA  CENTRAL 
HIGH  SCHOOL.  ETC. 


THIRD  EDITION. 

THOROUGHLY  REVISED 
BY 

HARRY  F.    KELLER,   PH.D., 

PROFESSOR  OF  CHEMISTRY  IN  THK  PHILADELPHIA  CENTRAL  HIGH  SCHOOL. 


PHILADELPHIA  I 

J.  B.  LIPPINCOTT   COMPANY. 

LONDON:. 36  SOUTHAMPTON  STREET,  COVENT  GARDEN. 


Copyright,  1884,  by  J.  B.  LIPPINCOTT  COMPANY. 


Copyright,  1898,  by  J.  B.  LIPPINCOTT  COMPANY. 


Copyright,  1909-  bv  J.  B.  LIPPINCOTT  COMPANY. 


TABLE  OF  CONTENTS. 


E^— Introjjoietwm^ Chemical  Phenomena    . 

Irogen      ........ 

^Oxygen — Combustion  .         .         . 

mposition  of  Water — Chemical  Laws  and  Theories 
iws  of  Combination — Atomic  Theory 

ies  of  Water— Potable  and  Mineral  Waters 
. — Chemical  Nomenclature — Ozone — Hydrogen  Dioxide 


PAGE 
» 

,  16 
23 
32 
38 
45 
50 
57 

Acid— Acids— Salts 62 

/^X. — Bromine — Iodine— Fluorine          ...„., 

XL— Sulphur— Hydrogen  Sulphide       ....  „      "lT3 

XII.— Sulphur  Dioxide— Sujphur  Trioxide    .  ...      79 

XIIL— Sulphuric  Acid     . .82 

XlV^-Sulphates 87 

-NitrogenT^The  Atmosphere — Argon  in  1  its  Companions     .       91 

[. — Ammonia  and  its  Compounds 97 

XVII. — Ammonium  Compounds — Nitrogen  Iodide  .         .         .     101 

XV^fl.— Nitrous  Oxide— Nitric  Oxide 104 

Xlg^Nitrogen  Peroxide— Nitrogen  Pentoxide      .         .         .         .108 

XlXX-Nitric  Acid 112 

XXL— Nitrates         .     ' 116 

XXIL— Phosphorus^Hydrogen  Phosphide 119 

XXIIL— Oxides  and  Acids  of  Phosphorus 123 

XXIV.— Arsenic— Compounds  and  Tests 128 

XXV.— Antimony     .    ' 134 

XXVL— Boron 137 

XXVIL— Silicon— Glass 140 

XXVIIL— Carbon          . 144 

XXftfT^Oxides  of  Carbon 150 

XXX.— Carbonates 156 

XXXL— Carbon  Disulphide— Cyanogen 162 

XXXII.— Hydrocyanic  Acid— Cyanides 166 

XXXIIL— Cyanates— Urea 171 

XXXIV. — Compounds  of  Carbon  and  Hydrogen  (1) 

Methane  and  Saturated  Hydrocarbons     ....     175 

235383  8 


TABLE    CF   CONTENTS. 


LESSON  PAGE 

XXXV.— Compounds  of  Carbon  and  Hydrogen  (2) 

Petroleum — Unsatur cited  Hydrocarbons     .         .       .  ••  •      .  181 
XXXVI. — Compounds  of  Carbon  and  Hydrogen  (3) 

Aromatic  Hydrocarbons — Elementary  Analysis       .         .186 

XXXVII.— Methyl  and  Ethyl  Alcohols— Alcoholic  Beverages       .         .  192 

XXXVIII.— Alcohols— Gly  cols— Glycerol 197 

XXXIX.— Simple  Ethers 201 

XL. — Aldehydes — Carbon  Acids — Acetone 206 

XLI. — Ethereal  Salts — Fatty  Acids — Saponification     .         .         .  211 
XLII.— Lactic,  Oxalic,  Tartaric,  and  Citric  Acids  .         .         .         .218 

XLIIL— Carbohydrates .,        .'        .  220 

XLIV. — Benzene  Derivatives,  Phenol,  Nitrobenzene,  Aniline  .         .  226 
XLV. — Benzene  Derivatives,  Benzoic,  Salicylic,  Gallic,  and  Tan- 

nic  Acids — Camphors — Indigo       .....  230 

XLVL— Natural  Alkaloids 236 

Xlfcwf.— Metals— Spectrum  Analysis 241 

XLVIII.— Metallic  Compounds— Specific  Heat    .         .         .         .         .  246 

XLIX.— Lithium— Sodium— Potassium 250 

L.— Silver 257 

LI.— Calcium— Strontium— Barium     .         .     /.         .         .         .265 

LIL— Lead /   .        .        .        .272 

LIII. — Magnesium — Zinc — Cadmium 277 

LIV.— Copper        .        ..,.-.        „,.        .        .        .        .283 

LV.— Mercury 290 

LVL— Bismuth  and  Gold 295 

LVIL— Aluminium 301 

LVIII.— Iron  and  its  Metallurgy 307 

LIX. — Compounds  of  Iron    . 315 

LX.— Cobalt— Nickel— Manganese 319 

LXL— Chromium  and  Tin     .         .         .         .         .         .         .         .  325 

LXIL— Platinum  and  its  Allied  Metals 331 

L2<*6.— The  Chemistry  of  Life 334 

APPENDIX. 

I. — Crystallography .  341 

II. — Stereochemistry 346 

Index                                                                                                         .         .  349 


PREFACE  TO  THE  THIRD  EDITION, 


OP  new  matter  comparatively  little  has  been  introduced  in 
this  edition.  Nevertheless  the  book  has  been  carefully  revised, 
and  numerous  changes  have  been  'made.  Most  conspicuous 
among  these  is  the  replacement  of  the  frontispiece  by  an  entirely 
new  plate  of  spectra  which,  it  is  believed,  is  greatly  superior  to 
the  old  one,  and  includes  also  the  more  characteristic  spectra  of 

gaseous  elements. 

H.  F.  K. 

PHILADELPHIA,  April,  1900. 


PREFACE  TO  THE  SECOND  EDITION. 


IN  preparing  the  present  edition,  the  aim  has  been  chiefly  to 
make  such  corrections  and  additions  as  were  rendered  necessary 
by  the  rapid  advance  of  chemical  science  since  the  first  appear- 
ance of  this  book.  The  general  plan  and  arrangement,  which 
have  proved  satisfactory  in  the  experience  of  the  editor  as 
well  as  that  of  the  author,  have  not  been  materially  modified : 
a  few  of  the  chapters  have  been  partly  rewritten,  and  a  brief 
explanation  of  stereoisomerism  is  given  in  the  Appendix. 

H.  F.  K. 

PHILADELPHIA,  January,  1898. 


THE  DECIMAL  SYSTEM  OF  WEIGHTS  AND  MEASURES, 
AND  THE  CENTIGRADE  SCALE  OF  THE  THER- 
MOMETER, ARE  USED  IN  THIS  BOOK. 


CENTIGRADE    FAHRENHEIT 

SCALE.               SCALE. 

1  Metre           =  39.370708  inches. 

300° 

572° 

1  Centimetre  =    0.39370        " 

1  Millimetre  =    0.03937 

200° 
150° 

360° 

QAOO 

1  Inch             —    2.539954  centimetres. 

100° 

oUQi 

212° 

Water  boils. 

OUNCES  TROY               POUNDS 

90° 
80° 

194° 
176° 

=  480  GRAINS.      AVOIRDUPOIS. 

1  Milligramme    =         0.000032            0.0000022 

70° 

158° 

1  Centigramme  =         0.000321            0.0000220 

60° 

140° 

1  Decigramme    =          0.003215            0.0002204 

1  Gramme            =         0.032150            00022046 

50° 

122° 

1  Decagramme    =         0.321507            0.0220462 

40° 

104° 

1  Hectogramme  =         3.215072            0.2204621 

1  Kilogramme    =       32.150726            2.2046212 

30° 

86° 

1  Gramme  =  15.4323  grains. 

20° 

68° 

10° 

50° 

1  Grain                     =    0.064799  grammes. 

0° 

32° 

Water  freezes. 

1  Oz.  Troy               =  31.103496        " 

—10° 

14° 

f 

1  Lb.  Avoirdupois  —      .453593  kilogrammes. 

—17.8° 

0° 

1  Cubic  Centimetre  of  water  at  4°  weighs  1 

gramme. 

—20° 

—2° 

To  convert  centigrade  degrees  into  Fahrenheit 

—  30° 
—40° 

—  22° 
—40° 

Mercury  freeze 

degrees,  multiply  by  9,  divide  by  5,  arid  add  32°. 
To  convert  Fahrenheit  degrees  into  centigrade 
degrees,  subtract  32°,  then  multiply  by  5,  and 
divide  by  9 


A  dull  red  heat  is  about  500°  centi- 
grade, or  950°  Fahrenheit. 

A  high  red  heat  is  about  1000°  O, 
and  a  white  heat  about  1500°. 


LESSONS  IN  CHEMISTRY. 


LESSON    I. 

INTRODUCTION. 

Chemistry  is  the  science  which  studies  the  differences  of  different 
kinds  of  matter. 

1.  Substance. — Matter  occupies  space,  and  can  be  measured 
and  weighed.     The  different  kinds  of  matter  constitute  so  many 
different  substances,  which  are  distinguished  from  one  another  by 
general  properties,  such  as  color,  relative  weight,  hardness,  etc., 
and  no  two  substances  can  be  alike  in  all  properties. 

Some  substances  are  capable  of  existing  in  the  three  possible 
states,  as  solid,  liquid,  and  gas.  Water  is  the  most  common 
example  of  such  a  substance ;  by  the  action  of  more  or  less  heat 
it  can  be  converted  at  pleasure  into  steam,  liquid  water,  or  ice. 
However,  if  we  strongly  heat  a  piece  of  wood  or  some  sugar,  these 
substances  will  not  be  melted  into  liquids  or  changed  to  vapor,  but 
will  be  transformed  into  entirely  different  kinds  of  matter,  from 
which  we  cannot  again  obtain  the  original  substance. 

2.  Physical  Changes. — We  all  know  that  water  is  capable  of 
existing  in  many  forms :  mist,  fog,  rain,  frost,  snow,  sleet,  and  ice 
all  represent  the  same  substance,  and  we  know  that  these  forms 
may  change  one  into  another  while  otherwise  the  substance 
remains  unaffected.    The  salt  water  of  the  ocean  differs  from  the 
fresh  water  of  the  rivers  which  flow  into  it,  only  because  the  sea- 
water  contains  salt  and  other  forms  of  matter ;  but  these  substances 
are  not  water.     If  salt  water  be  boiled,  and  a  plate  or  other  cold 
surface  be  held  in  the  steam  given  off,  drops  of  water  will  condense 

7 


8  LESSONS   IN   CHEMISTRY. 

on  the  plate,  and  will  be  found  to  be  perfectly  fresh.  The  changes 
which  convert  ice  into  water,  or  water  into  steam  or  ice,  are  called 
physical  changes,  because  the  nature  of  the  substance  is  not 
affected  ;  a  little  more  heat,  or  a  little  less,  changes  the  water  into 
steam  or  ice,  or  the  steam  or  ice  back  again  to  water. 

3.  Chemical  Changes. — Water  may,  however,  undergo  other 
changes,  in  which  its  nature  is  altered  and  new  substances  are 
produced.  Such  an  alteration  in  substance  is  a  chemical  change. 

Let  us  fill  a  test-tube  with  water,  and,  closing  the  open  end 
with  the  thumb,  invert  it  in  a  small  vessel  of  water.  Then  we 
wrap  a  morsel  of  sodium  (see  §  414)  about  as  large  as  a  pea,  in  a 
small  piece  of  wire  gauze,  twist  around  this  a  wire  which  may 
serve  as  a  handle,  and  now,  raising  the  tube  so  that  its  mouth  is 
just  below  the  surface  of  the  water,  we  push  the  gauze  under  the 
edge  of  the  tube  (Fig.  1).  A  small  piece  of  sodium  must  be  used, 


FIG 


for  the  experiment  is  often  ended  by  a  little  explosion,  which 
might  break  the  tube  if  a  large  piece  were  taken.  As  soon  as  the 
water  touches  the  sodium,  bubbles  of  gas  rise  to  the  surface  and 
are  collected  in  the  tube.  If  the  latter  be  not  quite  filled,  the 
gauze  may  be  withdrawn,  perfectly  dried  by  holding  it  in  a  flame, 
and  another  piece  of  sodium  introduced,  so  that  the  tube  shall  be 
quite  filled  with  gas.  When  this  is  accomplished,  we  may  raise 
the  tube  from  the  water,  still  carefully  holding  it  bottom  upwards, 


INTRODUCTION. 


9 


and  on  introducing  into  it  a  lighted  match  or  taper  the  gas  will 
take  fire,  but  will  extinguish  the  taper,  which  will,  however,  be 
relighted  by  the  burning  gas  as  it  is  withdrawn  (Fig.  2). 

We  shall  presently  learn  that  this  gas, 
which  is  called  hydrogen,  does  not  come 
from  the  sodium,  nor  does  it  contain  any 
sodium ;  it  must  therefore  be  produced 
from  the  water,  and  that  portion  of  the 
latter  which  has  yielded  the  hydrogen 
must  be  completely  altered  in  its  nature. 
The  change  is  called  a  chemical  reaction. 

4.  Elements   and  Compounds.— If 
water  is  thus  capable  of  yielding  another 
substance    produced    wholly   from    the 
water,  we  must  believe  that  water  is  a 
compound  substance,  composed  of  more 
than  one  kind  of  matter.     Of  the  in- 
numerable forms  of  matter  with  which 
we  are  familiar,  all,  excepting  compara- 
tively few,  are  compounds,  and  by  vari- 
ous means  may  be  converted  into  simpler 
forms. 

Chemists  are  acquainted  with  seventy- 
five  substances  which  they  have  been  unable  to  change  int> 
more  simple  forms.     These  substances  are  called  elements. 

5.  Mercuric  oxide  is  a  heavy,  red  powder.      We  introduce  *> 
small  quantity  of  this  powder  into  a  test-tube,  and  heat  it  in  the 
lame  of  a  spirit-lamp  or  Bunsen  burner  (Fig.  3).     We  will  first 
notice  that  its  color  darkens ;  but  this  change  is  only  physical,  for 
if  we  remove  the  tube  and  allow  it  to  cool,  the  original  color  is 
restored.     If,  however,  we  continue  to  heat  it,  in  a  shjrt  time  a 
bright  mirror  forms  on  the  glass  in  the  cooler  part  of  the  tube : 
we  now  light  a  splint,  allow  it  to  burn  for  a  moment,  and  then 
blow  it  out,  so  that  it  may  still  retain  a  spark  of  fire ,  on  intro- 
ducing this  spark  into  the  tube  it  at  once  bursts  into  flame,  and 
the  wood  is  relighted.    The  experiment  may  be  repoated  a  num- 


Fio.  2, 


10 


LESSONS   IN   CHEMISTRY. 


ber  of  times,  extinguishing  the  splint  and  relighting  it.  When 
we  have  sufficiently  studied  this  phenomenon,  we  may  examine  the 
tube,  and  we  will  find  that  the  mirror  in  the  interior  is  composed 
of  little  globules  of  metallic  mercury  ;  we  may  shake  them  out  and 
unite  them  in  one.  The  gas  which  has  been  given  off,  and  which 
causes  such  brilliant  combustion,  is  called  oxygen.  The  mercuric 

oxide  was  a  compound 
body.  By  the  aid  of 
heat  we  have  separated 
it  or  decomposed  it  into 
two  other  substances, 
— mercury  and  oxygen. 
Mercury  and  oxygen 
are  elements ;  chemists 
have  not  been  able  to 
convert  either  of  them 
into  other  substances 
of  simpler  nature. 

6.  Sulphur  and  cop- 
per are  also  elements. 
We  all  know  the  yellow 
color  and  brittleness  of 
sulphur,  and  the  red 
color  and  flexibility  of 
copper.  We  will  put 
into  a  test-tube  like  that  used  in  the  last  experiment  a  few  small 
pieces  of  sulphur,  and  on  top  of  them  some  copper  turnings  or  a 
bunch  of  copper  wire.  We  heat  the  tube ;  the  sulphur  melts,  and 
presently  begins  to  boil ;  but  in  a  few  moments  we  notice  that  the 
copper  becomes  very  hot,  much  hotter  than  the  portion  of  the 
tube  which  contains  only  sulphur.  A  chemical  phenomenon  is 
taking  place,  and  the  chemical  action  develops  great  heat.  When 
the  experiment  has  terminated,  we  allow  the  tube  to  cool,  break  it, 
and  find  that  it  no  longer  contains  copper,  and  unless  we  have 
used  too  much  sulphur  we  will  find  that  the  latter  also  has  dis- 
appeared. In  the  place  of  the  sulphur  and  copper  there  is  a  black, 


FIG.  3. 


INTRODUCTION.  11 

brittle  substance  which  resulted  from  the  chemical  union  of  the 
two  elements.  This  substance  is  called  copper  sulphide. 

In  our  first  experiment  we  have  seen  the  decomposition  of  a 
compound  ;  in  the  second  we  have  caused  the  combination  of  two 
elements.  Combination  is  the  union  of  two  or  more  substances 
to  form  a  more  complex  substance,  decomposition  the  separation 
of  one  substance  into  more  simple  substances  or  into  elements. 

If  we  were  to  carefully  collect  and  weigh  all  the  oxygen  and 
mercury,  we  would  find  the  weight  exactly  equal  to  that  of  the 
mercuric  oxide  from  which  they  were  obtained.  If  we  make  the 
second  experiment  in  a  long  tube  so  that  no  sulphur  vapor  may 
escape,  the  weight  of  the  tube  will  be  the  same  whether  it  contain 
sulphur  and  copper  or  copper  sulphide  resulting  from  their  union. 
Nothing  is  lost  or  gained  in  either  combination  or  decomposition. 

7.  Chemical  Combination  is  not  Mixture. — Mercuric  oxide 
is  not  a  mixture  of  oxygen  and  mercury,  nor  is  copper  sulphide  a 
mixture  of  copper  and  sulphur.    We  may  grind  the  last  two  sub- 
stances to  the  finest  powders  and  mix  them  together,  but  in  this 
mixture  we  can  by  the  aid  of  a  microscope  distinguish  the  parti- 
cles of  each  substance.    No  microscope  would  enable  us  to  detect 
sulphur  and  copper  in  the  black  copper  sulphide.     Since,  how- 
ever, we  can  separate  the  oxygen  from  the  mercury,  as  we  have 
seen,  and  the  sulphur  from  the  copper,  we  must  believe  that  the 
elements  still  exist  in  their  compounds. 

8.  Molecules, — We  know  that  under  certain  conditions  any 
substance  may  change  its  volume.   When  a  piece  of  iron  is  heated 
it  grows  larger  ;  when  it  is  cooled  it  becomes  smaller.    We  can- 
not believe  that  the  matter  of  the  iron  actually  increases  in  size 
when  it  is  warmed,  although  it  occupies  a  greater  volume.    We 
can  understand  this  change  in  volume  by  believing  that  there  are 
in  the  iron  spaces  or  pores  which  increase  in  size  when  the  metal 
expands,  and  grow  smaller  when  it  contracts.    These  pores  must 
be  very  small,  for  we  cannot  perceive  them  by  the  aid  of  the 
most  powerful  microscopes.    That  all  substances  must  be  porous, 
we  can  satisfy  ourselves  by  a  simple  experiment. 

We  have  a  glass  tube  about  a  foot  long,  closed  at  one  end,  and 


12  LESSONS   IN    CHEMISTRY. 

near  the  other  blown  out  in  two  bulbs,  and  the  part  between  the 
bulbs  is  rather  narrow  (Fig.  4).  We  pour  water  into  this  tube 
until  it  is  filled  to  the  top  of  the  lower  bulb.  The  water  has  been 
recently  boiled,  to  drive  out  the  air  which  was  dissolved  in  it. 
We  then  fill  the  remainder  of  the  tube  with  alcohol,  and  cork  it 
tightly ;  the  alcohol,  which  we  have  colored  with  a  little  aniline 
dye,  does  not  at  once  mix  with  the  water,  because  the  latter  is  the 
heavier.  We  now  invert  the  tube,  and  we  see  the  lighter 
alcohol  rise  through  the  water,  and  at  the  same  time  the 
two  liquids  become  thoroughly  mixed.  But  as  they  mix 
we  see  little  bubbles  forming,  and  there  is  presently  a  small 
empty  space  at  the  top  of  the  tube.  This  space  is  not  filled 
with  air ;  for  if  we  put  the  mouth  of  the  tube  under  water 
and  draw  the  cork,  the  water  will  rise  and  fill  the  tube. 
The  mixture  then  does  not  occupy  as  much  volume  as  the 
substances  before  mixture.  We  must  explain  the  experi- 
ment by  saying  that  the  water  and  alcohol  are  porous,  and 
that  the  water  runs  into  the  pores  of  the  alcohol,  and  the 
alcohol  into  the  pores  of  the  water. 

If  substances  be  in  this  manner  porous,  they  must  consist 
of  small  particles  which  are  separated  from  one  another  by 
spaces.  Both  spaces  and  particles  are  so  small  that  we 
can  never  hope  to  see  them,  but  we  have  reason  to  believe  that 
the  spaces  are  quite  large  in  comparison  to  the  particles  of  matter 
which  they  separate.  These  particles  are  called  molecules,  and  for 
our  purposes  of  study  we  may  consider  that  the  spaces  between 
them  are  perfectly  empty. 

9.  Atoms  and  Molecules. — The  little  particles  of  which  a 
chemical  substance  is  composed  are  called  molecules,  and  we  shall 
learn  reasons  for  believing  that  all  molecules  of  the  same  kind, 
that  is,  of  the  same  substance,  have  the  same  size  and  weight. 

The  kind  of  matter  in  a  molecule  must  be  the  same  as  that  in 
any  quantity  of  the  substance.  If  from  mercury  we  can  obtain 
only  mercury,  the  molecules  of  mercury  must  consist  of  that  ele- 
ment only ;  but  if  from  mercuric  oxide  we  can  obtain  both  mer- 
cury and  oxygen,  the  molecules  of  mercuric  oxide  must  contain 


INTRODUCTION.  13 

both  elements.  Hence  it  follows  that  there  must  be  particles 
still  smaller  than  molecules,  and  to  these  smallest  particles  we 
give  the  name  atoms.  Since  chemists  cannot  separate  oxygen 
into  any  other  substances,  we  believe  that  the  atoms  of  oxygen 
are  unalterable  by  any  known  force,  be  it  physical  or  chemical ; 
and  it  is  the  same  with  the  atoms  of  all  other  elements. 

10.  An  atom  is  the  ultimate  result  of  the  division  of  matter  ; 
it  is  the  smallest  particle  of  an  element  that  can  enter  into  com- 
bination.    The  nature  of  an  element  depends  upon  the  nature 
of  its  atoms. 

11.  A  molecule  may  consist  of  one  or  of  several  atoms  ;  in  the 
latter  case,  if  the  atoms  be  of  the  same  kind  the  molecule  will  be 
that  of  an  element  or  simple  body,  but  if  they  be  of  different 
kinds  the  molecule  must  be  that  of  a  compound.    The  molecules 
of  hydrogen  can  contain  only  atoms  of  hydrogen,  and  the  'mole- 
cules of  oxygen  must  consist  of  atoms  of  oxygen  only,  but  the 
molecules  of  water  contain  atoms  of  both  hydrogen  and  oxygen  ; 
those  of  copper  sulphide  contain  atoms  of  sulphur  and  of  copper. 

The  nature  of  a  substance  will  then  depend  upon  the  number 
and  kind  of  atoms  contained  in  its  molecules.  We  have  seen  that 
mercuric  oxide  contains  mercury  and  oxygen  :  let  us  pour  a  little 
nitric  acid  on  some  of  this  red  powder  contained  in  a  test-tube, 
and  warm  the  mixture  over  a  lamp.  The  mercuric  oxide  disap- 
pears, and  we  obtain  a  colorless  liquid  ;  if  we  pour  this  liquid  into 
a  flat  dish,  and  set  it  aside  in  a  warm  place,  we  will  find  after  a 
time  a  mass  of  white  crystals.  A  chemical  change  has  taken 
place :  while  dissolving  in  the  nitric  acid,  the  mercuric  oxide  has 
been  converted  into  mercuric  nitrate.  The  latter  body  contains 
mercury,  oxygen,  and  nitrogen,  and  its  molecule  must  consist  of 
atoms  of  each  of  those  elements :  the  new  molecule  is  more  com- 
plex than  that  of  mercuric  oxide,  which  contained  only  two  kinds 
of  atoms. 

12.  Chemical  Affinity. — The  force  which   unites  atoms  is 
called  affinity.     Its  energy  is  not  the  same  for  all  atoms,  and 
depends  on  many  conditions.    While  heat  may  aid  in  the  forma- 
tion of  a  compound,  as  in  the  case  of  copper  sulphide,  it  may  also 
cause  decomposition,  as  in  that  of  mercuric  oxide.    Other  forces, 


14  LESSONS   IN   CHEMISTRY. 

light  and  electricity,  may  act  in  the  same  manner,  in  one  case  pro- 
ducing combination,  and  in  another  decomposition :  in  every  case 
the  result  depends  upon  the  energy  with  which  the  atoms  of  the 
molecule  are  held  together.  Why  must  we  heat  the  copper  and 
sulphur  before  they  will  combine  ?  Simply  because  the  atoms  of 
sulphur  hold  strongly  together  in  the  molecules  of  sulphur,  and 
the  atoms  of  copper  in  the  molecules  of  that  metal:  we  must 
therefore  communicate  to  these  molecules  so  much  energy  in  the 
form  of  heat  that  the  atoms  of  sulphur  may  be  sufficiently  loosed 
from  each  other  to  catch  hold  of  the  atoms  of  copper.  Then  in- 
stead of  molecules  containing  atoms  of  sulphur  or  copper  only,  we 
have  others  containing  sulphur  and  copper. 

13.  We  mix  a  small  quantity  of  powdered  cupric  oxide,  a  black 
compound  containing  only  copper  and  oxygen,  with  about  one- 
seventh  its  weight  of  powdered  charcoal,  and  heat  the  mixture 
in  a  test-tube.      When  the  mixture  becomes  hot,  we  see  that 
the  black  color  changes  to  reddish  brown :  after  the  powder  has 
cooled,  we  turn  it  out,  and  find  that  it  is  very  finely  divided 
copper.     We  cannot  'heat  the  cupric  oxide  alone  hot  enough  to 
decompose  it ;  but  the  charcoal,  which  is  an  element,  has  a  strong 
affinity  for  the  oxygen,  and  easily  takes  it  away  from  the  copper. 

The  charcoal  and  oxygen  combine  together  and 
form  a  gas  called  carbon  dioxide,  which  passes 
out  of  the  tube.  We  can  prove  that  some 
new  gas  is  formed  during  the  experiment,  for 
if  we  push  a  lighted  match  into  the  mouth  of 
the  tube  while  it  is  being  heated,  the  flame 
will  be  extinguished,  an  effect  exactly  oppo- 
site to  that  which  was  produced  while  heat- 
ing the  mercuric  oxide.  We  then  explain  the 
experiment,  which  is  at  the  same  time  a  com- 
bination and  a  decomposition,  by  saying  that 
the  oxygen  has  a  stronger  affinity  for  the  char- 
coal than  for  the  copper. 

14.  Into  a  jar  or  glass  nearly  filled  with  water  (Fig.  5)  we 
pour  first  a  few  drops  of  a  solution  of  mercuric  chloride,  and  then 


INTRODUCTION.  15 

some  solution  of  potassium  iodide.  At  once  a  pink  or  red  pre- 
cipitate is  formed,  showing  that  a  chemical  change  has  taken 
place.  Both  mercuric  chloride  and  potassium  iodide  are  color- 
less :  the  first  contains  two  elements,  mercury  and  chlorine,  while 
the  second  also  contains  two,  potassium  and  iodine.  The  chemical 
change  takes  place  because  the  affinities  of  potassium  for  chlorine, 
and  of  mercury  for  iodine,  are  stronger  than  those  of  potassium 
for  iodine,  and  of  mercury  for  chlorine.  Consequently  both  the 
original  substances  are  decomposed,  and  two  new  substances  are 
formed,  mercuric  iodide,  which  is  insoluble  (unless  too  much  of 
either  substance  has  been  used),  and  potassium  chloride,  which 
remains  dissolved  in  the  liquid.  This  is  an  example  of  double 
decomposition,  the  most  common  kind  of  chemical  change.  A 
comparison  will  show  that  it  closely  resembles  the  double  decom- 
position between  sulphur  molecules  and  copper  molecules  already 
explained  (§  12). 

15.  Chemical  affinity  is  not  to  be  regarded  as  a  special  force, 
but  only  as  one  form  of  energy ;  it  is  manifested  between  atoms, 
which  it  holds  together  in  the  molecules,  just  as  these  molecules 
are  held  together  by  the  force  of  cohesion.     Affinity  depends  not 
only  on  the  kind  of  atoms  between  which  it  is  exerted,  but  on  the 
temperature :  elements  which  have  strong  affinities  for  each  other 
at  a  given  temperature  may  not  manifest  such  affinities  at  other 
temperatures. 

16.  Metals  and  Non-Metallic  Elements. — For  convenience 
of  study  the  elements  are  generally  divided  into  two  classes,  metals 
and  non-metals.    The  reasons  for  which  an  element  is  considered 
to  be  a  metal  or  a  non-metal  will  be  understood  when  we  shall 
have  progressed  farther,  but  we  will  then  learn  that  the  classifi- 
cation is  more  for  convenience  than  because  of  any  absolutely 
special  properties  of  either  class. 

Many  of  the  elements  are  quite  rare,  and  are  seldom  seen  even 
by  chemists  ;  others  are  abundant  and  widely  distributed.  A 
list  of  those  thus  far  discovered  will  be  found  in  the  table  on 
page  44. 


Chlorine. 

Metargon. 

Silicon. 

Fluorine. 

Neon. 

Sulphur. 

Helium. 

Nitrogen. 

Tellurium. 

Hydrogen. 

Phosphorus. 

Xenon. 

Iodine. 

Oxygen. 

Krypton. 

Selenium. 

16  LESSONS   IN    CHEMISTRY. 

The  names  of  the  non-metals  are  as  follows  : 

Antimony. 

Argon. 

Arsenic. 

Boron. 

Bromine. 

Carbon. 

Because  they  resemble  one  another  in  important  properties, 
certain  of  these  elements  are  classed  together  in  natural  families. 
We  will  be  better  able  to  understand  these  relations  when  we 
have  studied  some  of  the  compounds,  and  have  seen  how  all 
chemical  changes  through  which  these  compounds  may  pass  can 
be  explained  by  our  theory  of  atoms  and  molecules.  At  the 
same  time  we  will  find  that  our  study  will  greatly  enlarge  and 
render  more  definite  the  ideas  which  we  have  already  acquired. 


LESSON    II. 
HYDROGEN. 

17.  A.S  we  have  already  seen,  hydrogen  is  one  of  the  elements 
of  wai^r,  of  which  it  constitutes  one-ninth  by  weight.     It  exists 
in  combination  with  other  elements  in  all  animal  and  vegetable 
substances,  in  coal,  and  in  the  natural  oils,  petroleum  and  pitch. 

In  our  first  experiment  (§  3)  we  have  studied  one  method  by 
which  it  may  be  obtained, — the  action  of  the  metal  sodium  on 
water.  That  method  is  unsuitable  for  the  preparation  of  any  but 
very  small  quantities  of  hydrogen ;  when  it  is  desired  to  prepare 
the  gas  from  water,  steam  may  be  passed  over  red-hot  iron. 
The  metal  then  combines  with  the  oxygen  of  the  water,  setting 
free  the  hydrogen. 

18.  Preparation, — In  the  laboratory,  hydrogen  is  made  by 
the  reaction  of  zinc  with  hydrochloric  acid  or  sulphuric  acid 
diluted  with  water. 


HYDROGEN. 


17 


We  put  in  the  bottom  of  a  tall  jar  (Fig.  6)  some  small  pieces  of 
very  thin  sheet  zinc,  or 
a  handful  of  granulated 
zinc,  and  on  this  pour 
some  hydrochloric  acid. 
A  brisk  effervescence 
begins ;  when  we  apply 
a  flame  at  the  mouth  of 
the  jar,  the  gas  which  is 
disengaged  at  once  takes 
fire,  and  a  large  stream 
of  very  pale  flame  shoots 
into  the  air. 

This  gas  is  hydrogen. 
Hydrochloric  acid  is  a 
compound  of  chlorine 
and  hydrogen  ;  when  it 
acts  on  zinc,  that  metal 
drives  the  hydrogen  out 
of  its  combination,  and 
unites  with  the  chlorine, 
forming  a  new  com- 
pound, called  zinc  chlo- 
ride. We  may  express  the  chemical  change  as  follows : 


FIG.  6. 


BEFORE  THE  REACTION.  AFTER  THE  REACTION. 

Hydrochloric  acid  +  Zinc         =         Zinc  chloride  +  Hydrogen 

containing  containing 

Hydrogen  +  Chlorine  Zinc  +  Chlorine 

Dilute  sulphuric  acid  is  usually  employed  instead  of  hydro- 
chloric acid  for  the  preparation  of  hydrogen.  We  may  explain 
the  change  in  a  similar  manner : 

+  Zinc         =         Zinc  sulphate          +  Hydrogen 


Sulphuric  acid 

containing 
Sulphur  +  Oxygen  +  Hydrogen 


=         Zinc  sulphate 

containing 
Sulphur  +  Oxygen  +  Zinc 


It  is  sufficient  to  put  the  zinc  in  a  bottle,  and,  after  pouring  in 
the  dilute  sulphuric  acid,  to  close  the  mouth  of  the  bottle  with  a 

\  2 


18 


LESSONS   IN   CHEMISTRY. 


FIG.  7. 


cork  through  which  passes  a  tube  for  the  exit  of  the  gas  ;  but  it 
is  more  convenient  to  have  a  cork  with  two  holes,  or  a  bottle  with 
two  necks.  Into  such  a  bottle  (Fig.  7)  we  will  introduce  some 
granulated  zinc  that  has  been  made  by  melting 
zinc  and  pouring  it  from  a  little  height  into  a 
bucket  of  water.  Then  we  adapt  to  one  of  the 
necks  of  the  bottle  a  cork  through  which  passes  a 
long  tube  with  a  funnel  at  the  upper  end ;  the 
lower  end  of  this  tube  must  pass  nearly  to  the 
bottom  of  the  bottle,  so  that  it  may  dip  into  the 
liquid  and  no  gas  may  escape  by  it.  To  the  other 
neck  we  adapt  a  cork  bearing  a  tube  bent  at  right 
angles,  and  this  serves  for  the  passage  of  the  gas. 
Over  the  end  of  this  tube  we  may  pass  a  rubber 
pipe  and  lead  the  gas  wherever  we  wish  it.  We 
now  pour  through  the  funnel-tube  some  sulphuric 
acid  which  -we  have  diluted  with  about  five  times 
its  volume  of  water  and  allowed  to  cool,  for  sul- 
phuric acid  becomes  very  hot  when  it  is  mixed  with  water,  and 
we  always  make  the  mixture  by  pouring  the  acid  into  the  water, 
and  not  the  water  into  the  acid.  The  effervescence  shows  us  that 
gas  is  being  disengaged,  and,  after  waiting  a  few  moments  to  allow 
the  hydrogen  time  to  drive  all  the  air  out  of  the  bottle,  we  may 
make  some  experiments  with  our  gas.  These  experiments  will 
make  us  acquainted  with  its  properties. 

19.  Properties  of  Hydrogen.— Hydrogen  is  a  colorless  gas, 
and  has  neither  taste  nor  odor,  as  we  can  determine  by  examining 
it  as  it  escapes  from  the  tube.  It  is  the  lightest  substance  known. 
We  connect  our  gas-generating  bottle  with  the  rubber  pipe,  the 
other  end  of  which  is  passed  over  a  straight  glass  tube,  and  push 
this  tube  up  to  the  bottom  of  a  wide  test-tube  which  is  turned  up- 
side down  (Fig.  8).  In  a  short  time  this  little  jar  is  filled  with 
hydrogen,  for  the  gas  is  so  light  that  it  collects  in  the  jar,  and 
pushes  the  air  down  and  out  at  the  mouth.  We  can  prove  that 
the  jar  is  filled  with  hydrogen,  for  when  we  withdraw  the  tube 
and  introduce  a  lighted  taper,  the  gas  at  once  takes  fire  and  burns 


HYDROGEN. 


19 


FIG.  8. 


at  the  mouth  of  the  jar ;  the  taper  is  extinguished  on  entering  the 

gas,  but  is  relighted  as  it  is  draw  a  out  through  the 

hydrogen  flame.     The  hydrogen  is  collected  in  this 

case  by  upward  dry  displacement :  it  displaces  the  air. 

We  again  fill  our  tube  with  hydrogen  in  the  same 

manner,  and  taking  another  and  smaller  tube  we  place 

it  alongside  of  the  first,  which  we  carefully  incline 

(Fig.  9)  more  and  more  until  we  have  poured  all  the 

hydrogen  up  into  the  second  jar.     On  introducing 

a  lighted  taper  into  the  latter,  the  gas  takes  fire  and 

burns  with  a  slight  explosion,  for  while  flowing  out  of 

the  first  vessel  it  became  mixed  with  a  little  air. 

On  account  of  its  lightness,  hydrogen  is  often  used 
to  fill  balloons;  soap-bubbles,  which  may  be  easily 
made  by  dipping  the  end  of  the  tube  into  suds,  will 
rise  quickly  in  the  air  when  they  are  shaken  from  the  tube. 

A  given  volume  of  hydrogen  is  only  0.0695  as  heavy  as  the 
same  volume  of  air :  this  is  expressed  by  saying  that  the  density 
of  hydrogen  compared  to  air  is 
0.0695 ;  for  equal  volumes,  air  is 
then  14.388  times  as  heavy  as  hy- 
drogen. One  litre  of  hydrogen 
measured  at  0°  (the  freezing  point 
of  water),  and  under  the  ordinary 
pressure  of  the  atmosphere,  weighs 
0.0899  of  a  gramme. 

20.  The  diffusibility  of  a  gas  is 
its  tendency  to  mix  with  other 
gases :  gases  will  mix  with  one  an- 
other in  this  manner  even  through 
the  pores  of  many  substances  which 
are  sensibly  porous,  that  is,  possess 
pores  large  enough  to  be  seen  by  the  aid  of  a  microscope.  It 
has  been  found  that  the  diffusibility  of  gases  depends  upon  their 
densities.  The  lighter  a  gas  is,  the  more  diffusible  is  it  also,  and, 
on  the  contrary,  the  heavier  gases  do  not  diffuse  as  quickly  as  the 


FIG.  9. 


20 


LESSONS   IN    CHEMISTRY. 


FIG.  10. 


lighter  ones.  Since  hydrogen  is  the  lightest  gas,  we  can  under 
stand  that  it  must  be  the  most  diffusible :  we  allow  a  little  hydro- 
gen to  escape  into  the  air,  and  in  a  few  seconds  it  scatters  through 
all  the  air  in  the  room. 

We  have  arranged  another  tube  through  which  the  hydrogen 
may  escape  from  our  gas-bottle,  and  this  tube  is  drawn  out  so  that 
it  has  a  small  opening  at  which  we  may 
burn  the  gas  if  we  desire.  Close  above 
the  unlighted  gas  escaping  from  this  jet 
we  hold  a  piece  of  paper  (Fig.  10) ;  the 
hydrogen  passes  through  the  paper,  as  we 
prove  by  igniting  it  above,  and  the  flame 
of  the  gas  quickly  sets  fire  to  the  paper 
and  passes  through  to  the  gas  at  the  jet. 

Because  it  is  so  diffusible,  hydrogen 
cannot  be  kept  in  bottles  which  have  the 
smallest  cracks.  It  even  passes  through  hot  plates  of  iron  and 
platinum. 

21.  Hydrogen  is  almost  insoluble  in  water,  and  may  be  col- 
lected over  the  pneumatic  trough  by  wet  displacement.  Gases 
which  are  but  slightly  soluble  in  water  may  be  collected  in 

this  manner:  the  jar  in  which  we 
wish  to  receive  the  c;as  is  filled 
with  water  and  inverted  in  a 
trough  near  the  top  of  which  is 
a  shelf  on  which  the  jar  may  rest. 
The  water  will  not  run  out  of  the 
jar  as  long  as  the  mouth  of  the 
latter  is  below  the  surface.  Under 
the  edge  of  this  jar  filled  with 
water  we  pass  the  end  of  the  tube 
from  which  escapes  the  gas  that 
we  wish  to  collect ;  this  gas  bub- 
bles up  through  the  water,  which  it  drives  out  of  the  jar  (Fig. 
11).  If  it  be  desired,  we  can  transfer  the  gas  from  one  jar  to 
another,  by  first  filling  the  second  jar  with  water,  placing  it  on 
the  trough,  and  then  pouring  the  gas  up  through  the  water  by 


FIG.  11. 


HYDROGEN.  21 

inclining  the  jar  which  contains  it  under  the  edge  of  that  which 
is  to  receive  it. 

22.  Of  all  the  known  gases,  hydrogen  is  the  best  conductor  of 
heat.     We  have  fitted  to  the  ends  of  a  glass  tube  (Fig.  12)  two 
tightly  -  fitting       corks 

through  each  of  which 
passes  a  smaller  tube, 
and  also  a  thick  wire 

which  is  connected  with 

i  i  ^* 

a  voltaic    battery;    the 

two  wires  are  joined  by  a  thin  platinum  wire  which  becomes 
heated  red-hot  by  the  electric  current.  We  can  now  pass  any 
gas  through  this  tube  and  notice  the  effect  on  the  wire ;  we  try 
oxygen,  nitrogen,  carbon  dioxide,  and  see  that  the  wire  still  re- 
mains red-hot ;  but  when  we  pass  hydrogen  through  the  tube  the 
wire  ceases  to  glow.  The  hydrogen  has  conducted  away  the  heat. 
By  exposing  it  to  the  extremely  low  temperature  of  about  250 
degrees  below  0,  hydrogen  has  been  converted  into  a  liquid,  and 
at  still  lower  temperatures  into  a  solid.  Liquid  hydrogen  is  clear 
and  colorless,  and  its  density  is  only  TJ¥  that  of  water. 

23.  We  have  seen  (§  19)  that  hydrogen  will  burn  in  air,  and 
that  it  will  not  support  combustion  ;  the  burning  taper  was  ex- 
tinguished by  hydrogen.     When  it  burns,  hydrogen  combines 
with  the  oxygen  of  the  air,  forming  vapor  of  water ;  this  is  the 
sole  product  of  the  combustion  of  hydrogen.     We  may  assure 
ourselves  of  this  by  holding  over  a  jet  of  burning  hydrogen  an 
inverted  jar,  of  which  the  interior  will  rapidly  become  covered 
with  little  drops  of  dew,  and  these  will  soon  unite  together  and 
trickle  down  the  sides  of  the  jar.    This  takes  place  with  hydro- 
gen which  has  been  perfectly  dried  by  passing  through  a  tube 
containing  calcium  chloride,  or  pumice-stone  wet  with  sulphuric 
acid  (Fig.  13)  ;  both  these  substances  remove  all  moisture  from 
gases  with  which  they  come  in  contact. 

If  hydrogen  be  mixed  with  half  its  volume  of  oxygen,  or  about 
three  times  its  volume  of  air,  the  mixture  will  explode  violently 
when  ignited.  For  this  reason  we  must  be  careful  that  all  the 
air  has  been  driven  from  the  generating  bottle  before  lighting  the 


22 


LESSONS   IN   CHEMISTRY. 


hydrogen.     We  may  make  the  explosion  harmlessly  by  passing  a 
little  hydrogen  into  a  hydrogen  pistol,  made  of  sheet  tin,  and,  after 

6 


FIG.  14. 


FIG.  13. 

corking  the  mouth  of  the  pistol,  ignite  the  mixed  gases  by  holding 
a  flame  to  the  little  hole  at  the  other  end  ; 
the  cork  is  then  driven  out  with  a  loud 
noise  (Fig.  14) :  while  charging  the  pistol, 
we  must  close  the  hole  with  the  finger. 
If  we  slip  over  a  small  jet  of  burning 

hydrogen  a  rather  wide  glass  tube  (Fig.  15),  we  will  find  that 
when  the  flame  has  reached  a  certain  point 
in  the  wide  tube  it  begins^  to  quiver,  and  a 
more  or  less  musical  tone  is  produced.  The 
tone  may  be  varied  by  using  tubes  of  differ- 
ent lengths :  it  is  caused  by  the  current  of 
air  ascending  the  tube. 

24.  Certain  very  finely  divided  metals 
have  the  power  of  absorbing  hydrogen  so 
rapidly  as  to  become  hot  enough  to  light  the 
gas.  Spongy  platinum  is  such  a  substance  ; 
when  a  small  piece  of  this  very  porous  form 

of  platinum,  tied  by  a  thin  wire  in  the  centre 
FIG.  15.  of  a  gma]1  bragg  ring  (Fig  16^  ig  held  in  a 

jet  of  escaping  hydrogen,  it  becomes  bright  hot  and  the  gas  is 
inflamed.     The  spongy  platinum  should  be  heated  shortly  before 


OXYGEN. — COMBUSTION.  23 

making  the  experiment.  It  is  not  hard  to  understand  this  phe- 
nomenon, for  when  the  platinum  absorbs 
the  hydrogen  the  gas  is  necessarily  re- 
duced to  a  small  volume  in  the  pores  of 
the  metal,  and  the  heat  which  keeps  the 
molecules  of  the  gas  at  large  distances 
from  each  other  must  raise  the  tempera- 
ture when  those  distances  are  diminished 
by  the  condensation ;  just  as  the  heat 
which  converts  water  into  steam  reap-  FIG.  16. 

pears  when  the  steam  is  condensed. 

Hydrogen  combines  with  many  of  the  other  elements,  but 
under  ordinaiy  circumstances  its  affinities  are  not  very  pro- 
nounced. Heat  is  required  to  bring  about  the  union  of  hydro- 
gen and  oxygen.  Hydrogen  and  chlorine  combine  under  the 
influence  of  light  (see  §  73).  Pure  hydrogen  is  not  poisonous, 
but  it  does  not  support  respiration  (see  §  33). 


LESSON    III. 
OXYGEN.— COMBUSTION. 

25.  Oxygen  was  discovered  by  Scheele  and  independently  by 
Priestley  in  1774.    It  is  the  most  abundant  element  at  the  surface 
of  the  earth ;  it  forms  about  one-fifth  of  the  atmosphere,  in  which 
it  exists  uncombined,  but  mixed  with  the  element  nitrogen  and 
other  gases ;  its  combination  with  hydrogen  is  water,  and  it  enters 
largely  into  the  composition  of  nearly  all  minerals  and  rocks. 

We  have  seen  (§  5)  that  oxygen  is  produced  when  mercuric 
oxide  is  heated ;  but  this  method  would  be  too  expensive  for  the 
preparation  of  large  quantities  of  oxygen. 

26.  Preparation. — The  most  convenient  process  for  obtaining 
oxygen  consists  in  heating  a  compound  of  chlorine,  oxygen,  and 
potassium,  called  potassium  chlorate.     This  is  a  white,  crystalline 


LESSONS   IN    CHEMISTRY. 


substance,  from  which  heat  drives  out  all  the  oxygen,  leaving  a 
compound  of  potassium  and  chlorine,  called  potassium  chloride. 

We  put  a  little  potassium  chlorate  in  a  test-tube,  and  heat  it 
rather  strongly  in  the  flame  of  a  spirit-lamp  or  Bunsen  burner. 

It  melts,  and  soon  begins  to 
boil ;  this  boiling  is  the  es- 
cape of  the  oxygen,  as  we 
can  prove  by  pushing  into 
the  tube  a  match-stick  bear- 
ing a  spark  of  fire,  which 
instantly  bursts  into  flame 
(Fig.  17).  The  white  sub- 
stance which  remains  in  the 
tube  after  all  the  oxygen 
is  driven  out,  is  potassium 
chloride. 

When  we  wish  to  make 
and  collect  larger  quantities 
of  oxygen,  we  mix  the  po- 
tassium chlorate  with  about 
one-eighth  its  weight  of 
FIG.  17.  manganese  dioxide,  which 

causes  the   gas  to  be  given 

off  at  a  lower  temperature,  and  with  less  danger  of  explosion.  The 
manganese  dioxide  is  a  black  powder,  and  is  found  unaltered  after 
the  experiment,  being  simply  mixed  with  the  potassium  chloride : 
it  helps  the  reaction  because  it  has  an  affinity  for  oxygen  ;  but 
this  affinity  is  so  feeble  that  the  new  compound  which  is  formed 
is  at  once  decomposed,  the  oxygen  being  given  off,  while  the  man- 
ganese dioxide  remains  as  it  was  at  first.  We  may  consider  that 
it  pulls  the  oxygen  away  from  the  potassium  chlorate. 

We  introduce  our  mixture  of  potassium  chlorate  and  manganese 
dioxide  into  a  glass  flask,  to  which  we  adapt  a  tightly-fitting  cork 
bearing  a  tube  for  the  exit  of  the  gas.  Then  we  place  the  flask 
on  some  dry  sand  in  a  little  tin  or  sheet-iron  dish,  which  we  call 
a  sand-bath,  and  under  this  we  place  a  lamp.  The  sand  becomes 


OXYGEN. —  COMBUSTION. 


25 


hot  and  heats  the  flask  gradually,  and  generally  prevents  cracking 
of  the  glass.     We  may  now  slip  a  rubber  tube  over  the  delivery- 


FIG.  18. 

tube  of  the  flask,  and  when  oxygen  begins  to  come  off,  as  we  may 
ascertain  by  holding  a  lighted  match  near  the  end  of  the  tube,  we 
may  collect  the  gas  in  a  jar  over  the  pneumatic  trough  (Fig.  18). 

As  glass  flasks  often 
break  in  this  experiment, 
when  we  want  many  litres 
of  oxygen,  we  heat  the 
generating  mixture  in  a 
flask  made  of  tightly 
lapped  sheet  copper  or 
tin  plate.  As  little  parti- 
cles of  manganese  dioxide 
are  carried  out  with  the 
gas,  we  usually  wash  the 
latter  by  making  it  pass 
through  some  water  in  a  wash-bottle.  The  whole  apparatus  is 
shown  in  Fig.  19. 

When  all  the  oxygen  has  been  disengaged,  we  remove  the  end 
of  the  tube  from  the  water  in  the  trough  before  taking  the  heat 
from  under  the  flask :  otherwise  water  would  be  drawn  back  as  the 
retort  cools,  and  would  break  a  glass  flask,  and  the  steam  might 
burst  one  of  tin  or  copper.  This  precaution  is  observed  in  the 
preparation  of  all  gases  made  by  the  aid  of  heat. 


FIG.  19. 


26  LESSONS   IN   CHEMISTRY. 

After  filling  several  jars  with  oxygen,  we  remove  them  from  the 
trough  by  passing  a  saucer  under  the  mouth  of  each,  below  the 
surface  of  the  water ;  then  on  lifting  them  out,  the  water  in  the 
saucer  prevents  the  escape  of  the  gas.  We  can  now  turn  them 
quickly  mouth  upward,  still  keeping  covered  with  the  saucer,  and 
we  are  ready  to  study  the  gas.* 

27.  Properties, — Oxygen  has  neither  color,  taste,  nor  odor. 
When   freshly  made  from   potassium  chlorate  it  usually  has  a 
smoky  appearance  and  more  or  less  odor,  but  these  are  impurities, 
and  disappear  after  the  gas  has  stood  for  a  time  over  the  pneumatic 
trough.     It  is  a  little  heavier  than   the  air,  its  density  being 
1.1056  ;  one  litre  of  the  gas  at  0°,  and  normal  pressure,  weighs 
1.429  grammes.     It  is  almost  insoluble  in  water.     By  great  cold 
and  pressure  it  is  converted  into  a  transparent,  mobile  liquid, 
having  a  bluish  tint. 

Oxygen  manifests  energetic  affinity  for  most  of  the  other  ele- 
ments :  it  combines  with  some  of  them  at  ordinary  temperatures, 
and  with  others  by  the  aid  of  more  or  less  heat. 

28.  Combustion. — The   burning  of  wood,  coal,  illuminating 
gas,  oil,  and  other  substances  with  which  we  are  familiar,  is  only 
the  combination  of  those  bodies  with  the  oxygen  of  the  air.    Into 
a  small  tube  closed  at  one  end,  we  have  put  some  ferrous  oxalate, 
made  by  adding  oxalic  acid  to  a  solution  of  ferrous  sulphate,  and 
after  drawing  out  the  open  end  of  the  tube  so  as  to  leave  a  small 
thin  opening,  we  twisted  a  wire  about  the  tube,  and  heated  it 
until  no  more  gas  escaped  at  the  opening ;  we  then  sealed  the  thin 

end  of  the  tube  by  holding  it 
for  a  moment  in  the  flame. 
The  result  of  this  heating  has 
been  to  decompose  the  ferrous 
oxalate,  leaving  a  very  fine 

powder   of  iron   in   the    tube. 
"Fro   20 

We  now  break  this  tube,  and 

shake  out  the  powder,  which  instantly  takes  fire,  falling  in  a  shower 

*  Oxygen  gas  compressed  in  steel  bottles  can  now  be  procured  from  dealers 
in  chemicals :  it  is  conveniently  drawn  from  these  bottles  as  required  for  ex- 
periment. 


OXYGEN. — COMBUSTION.  27 

of  sparks  (Fig.  20),  if  our  tube  has  been  well  prepared.  The  iron 
has  combined  with  the  oxygen  of  the  air :  it  has  been  burned  into 
a  substance  called  iron  oxide.  Usually  it  is  necessary  to  heat  a 
combustible  substance  before  it  will  burn;  then  as  soon  as  the 
union  with  oxygen,  or  the  oxidation  as  we  call  it,  begins,  the 
chemical  action  develops  sufficient  heat  to  keep  the  temperature  so 
high  that  the  combustion  may  continue  without  further  aid. 

Only  one-fifth  of  the  air  is  oxygen,  and  we  shall  learn  that  the 
other  gases  with  which  that  oxygen  is  mixed  not  only  do  not  help, 
but  prevent  combustion :  pure  oxygen  should  then  support  com- 
bustion much  more  energetically  than  air,  and  we  have  seen  that 
oxygen  causes  a  spark  on  a  chip  of  wood  to  burst  into  flame. 

29.  We  wrap  a  copper  wire  around  a  piece  of  charcoal,  and 
fasten  the  other  end  of  the  wire  in  a  hole  in  a  piece  of  tin  plate 
large  enough  to  cover  the  mouth  of  one  of  our  jars.  After  hold- 
ing the  charcoal  in  a  flame  until  a  corner  of  it  becomes  red-hot, 
we  quickly  remove  the  saucer  from  the  jar  and  plunge  into  it  the 
charcoal,  which  remains  suspended  (Fig.  21).  Instantly  the  com- 
bustion grows  very  vivid,  and,  if  we  have  a  knotty  piece  of  char- 
coal, brilliant  sparks  are  thrown  off".  The  charcoal 
combines  with  the  oxygen  until  all  of  one  or  the  other 
is  used  up.  The  result  of  the  combination  is  a  gas 
called  carbon  dioxide,  and  if  we  put  a  lighted  taper 
into  the  jar  containing  it,  the  flame  will  be  extin- 
guished :  we  may  add  that  the  oxygen  also  has  been 
burned,  and  can  serve  for  no  other  combustion  as  long 
as  it  remains  combined  with  the  carbon. 

After  softening  a  steel  watch-spring  by  heating  it  in 
a  flame,  we  twist  it  into  a  coil,  one  end  of  which  we  fasten  in  a 
cork,  and  over  the  other  end  we  slip  the  split  end  of  a  piece  of 
match-stick ;  after  lighting  this  we  quickly  introduce  it  into  a 
bottle  of  oxygen  (Fig.  22).  The  flame  heats  the  iron  so  hot  that 
it  can  begin  to  burn,  and  the  oxidation  furnishes  heat  enough  for 
the  combustion  to  continue :  brilliant  stars  of  burning  steel  shoot 
out,  and  hot  drops  of  iron  oxide  fall  to  the  bottom  of  the  jar,  in 
which  it  is  well  to  leave  a  layer  of  water  to  prevent  breaking. 


28 


LESSONS    IN    CHEMISTRY. 


FIG.  22. 


We  have  prepared  a  deflagrating-spoon  by  fastening  a  small 
saucer-like  piece  of  sheet  copper  on  the  end  of  a  straight  copper 
wire.  We  support  this  in  the  hole  in  our 
tin  plate,  and  on  a  little  dry  sand  which  we 
put  in  the  spoon  we  place  a  piece  of  phos- 
phorus (§  177)  a  little  larger  than  a  pea. 
We  light  the  phosphorus — it  takes  fire  very 
easily — and  plunge  the  spoon  into  a  new 
jar  of  oxygen  (Fig.  23).  At  once  a  most 
intense  light  is  produced  by  the  combustion 
of  the  phosphorus,  and  the  jar  becomes 
filled  with  a  white  smoke  of  phosphoric 
oxide,  the  compound  of  phosphorus  and 
oxygen.  After  a  time  this  smoke  dissolves  in  the  layer  of  water, 
which  we  leave  in  the  jar  for  this  experiment  as  for  the  last. 

The  metal  magnesium  burns  very  bril- 
liantly in  the  air :  we  twist  together  half 
a  dozen  ribbons  of  this  metal,  and,  after 
fastening  one  end  in  our  jar-cover,  we 
light  the  other  with  a  match.  On  intro- 
ducing this  into  a  jar  of  oxygen  the  in- 
tensity of  the  combustion  is  dazzling.  A 
white  smoke  of  magnesium  oxide  soon 
settles  in  the  jar,  arid  contains  of  course 
the  magnesium  and  oxygen  which  have 
combined  together.  The  jar  is  often 
broken  in  this  experiment. 

These  experiments  have  been  only  intense  cases  of  what  we 
commonly  call  combustion,  a  phenomenon  which  we  apply  for  the 
production  of  heat  and  light.  The  combustible  substances  ordi- 
narily employed,  such  as  wood,  coal,  illuminating  gas,  wax,  tallow, 
oil,  etc.,  contain  carbon  and  hydrogen ;  charcoal  is  almost  wholly 
carbon ;  these  substances  burn  because  the  carbon  and  hydrogen 
which  they  contain,  unite  readily  with  the  oxygen  of  the  air  when 
the  union  is  started  by  the  aid  of  heat. 

30.  The  brightness  of  the  light  is  not  always  proportional  to 


FIG.  23. 


OXYGEN. — COMBUSTION.  29 

the  amount  of  heat :  we  have  seen  that  the  flame  of  hydrogen  is 
very  pale,  but  it  is  very  hot.  If  we  desire  to  increase  the  heat  of 
a  fire,  we  furnish  the  combustible  with  more  oxygen  by  blowing 
air  into  it  with  a  bellows,  and  we  rake  the  ashes  from  our  coals  in 
order  that  the  oxygen  may  come  in  contact  with  the  hot  carbon : 
it  is  possible,  however,  to  furnish  too  much  air,  if  the  latter  be 
cold,  as  we  see  when  we  extinguish  a  candle-flame  by  blowing  on 
it.  When  we  want  the  most  intense  combustion  possible,  we 
supply  the  burning  body  with  pure  oxygen,  and  the  hottest  flame 
which  we  can  obtain  is  that  of  hydrogen  burning  in  oxygen.  This 
flame  is  that  of  what  is  called  the  oxyhydrogen  blow-pipe,  in  which 
a  tube  through  which  the  oxygen  is  forced  passes  inside  of  another 
tube  carrying  the  hydrogen ;  the  two  gases,  coming  from  separate 
gas-holders,  or  caoutchouc  bags,  mix  at  the  opening  of  the  jet  (Fig. 
24).  If  they  were  mixed  before  the  moment  of  burning,  the  ap- 


Oxygen. 


Hydrogen.  FlG.  24. 


paratus  containing  the  mixture  would  be  burst  by  the  explosive 
union  of  the  gases  (§  23).  In  using  the  oxyhydrogen  blow-pipe, 
we  first  turn  on  the  hydrogen,  light  it,  and  then  slowly  turn  on  the 
oxygen  until  we  have  the  hottest  flame.  If  it  be  inconvenient  to 
use  hydrogen,  we  may  substitute  for  it  illuminating  gas,  connect- 
ing by  a  rubber  tube  the  oxyhydrogen  blow-pipe  with  a  gas-fix- 
ture. While  the  oxyhydrogen  flame  is  not  very  bright,  it  is  very 
hot,  and  when  we  hold  in  it  a  piece  of  watch-spring,  or  an  old 
penknife-blade,  the  iron  is  burned,  making  a  brilliant  fountain  of 
fire.  The  metal  platinum,  which  does  not  melt  at  the  highest 
furnace  heat,  melts  readily  in  the  oxyhydrogen  flame. 

31.  Fire  is  the  combustion  with  incandescence — that  is,  pro- 
duction of  light  and  heat  at  the  same  time — of  a  solid  substance : 


30  LESSONS    IN    CHEMISTRY. 

we  have  seen  such  phenomena  in  the  combustion  of  charcoal  and 
iron.  The  oxidation  takes  place  only  on  the  surface  of  the  burn- 
ing body. 

32.  Flame  is  the  combustion  with  incandescence  of  a  gas  or 
vapor,  as  in  the  burning  of  hydrogen,  phosphorus,  and  magne- 
sium :  at  the  borders  of  the  flame  the  gas  or  vapor  may  mix  with 
the  air ;  but  the  interior  of  the  flame  must  consist  of  highly- 
heated,  yet  unburned  gas.  Why  are  certain  flames  very  bright, 
while  others  give  little  or  no  light  ?  We  burn  a  little  sulphur  in 
a  deflagrating-spoou  in  a  jar  of  oxygen,  and  the  combustion, 
though  very  brilliant,  would  not  serve  for  illumination.  In  order 
to  produce  a  bright  white  light,  a  flame  must  contain  particles  of 
solid  matter  which  may  become  highly  heated.  The  burning 
phosphorus  and  magnesium  were  brilliantly  luminous  because  the 
little  solid  particles  of  phosphoric  oxide  and  magnesium  oxide 
which  were  formed,  became  very  hot.  The  flames  of  hydrogen 
and  sulphur  do  not  give  white  light  because  the  products  of  com- 
bustion, water  in  one  case  and  sulphurous  oxide  in  the  other,  are 
gases  at  the  high  temperature  at  which  they  are  formed,  and 
gases  cannot  be  heated  hot  enough  to  give  white  light.  How- 
ever, the  products  of  combustion  of  tallow,  wax,  and  illuminating 
gas  are  not  solid,  yet  these  substances  are  useful  for  artificial  light. 
In  these  cases  the  illumination  is  due  to  little  particles  of  carbon. 
The  combustible  gases  and  vapors  come  in  contact  with  enough 
oxygen  to  completely  burn  them  only  on  the  outer  edge  of  the 
flame ;  but  the  heat  is  radiated  into  the  flame  as  well  as  from  it, 
and  the  gases,  which  are  compounds  of  hydrogen  and  carbon,  are 
decomposed ;  little  solid  particles  of  carbon  are  set  free,  and  these 
become  very  hot  and  give  out  light :  when  they  reach  the  outside 
of  the  flame  they  are  entirely  consumed,  unless  there  be  too  little 
oxygen,  and  in  that  case  the  flame  smokes.  When  a  cold  body — 
a  piece  of  glass  will  answer — is  held  for  a  moment  in  the  brightest 
part  of  a  lamp-  or  gas-flame,  the  little  particles  of  carbon  are  de- 
posited on  the  cold  surface  in  the  form  of  soot. 

We  may  by  a  very  simple  means  render  the  colorless  flame  of 
hydrogen  quite  brilliant :  we  have  fitted  to  a  bottle  a  cork  through 


OXYGEN. — COMBUSTION. 


31 


which  pass  two  tubes,  the  outer  ends  being  drawn  out  to  fine  jets. 
One  of  these  tubes  is  short,  and  passes  only  through  the  cork ; 
the  other  passes  to  the  bottom  of  the  bottle,  in  which  we  have 
placed  some  broken  pumice-stone  saturated  with  benzene  (Fig.  25). 
To  this  same  tube  is  joined  a  short  side-tube,  which 
we  connect  with  a  bottle  containing  zinc  and  dilute 
sulphuric  acid.  When  all  the  air  is  expelled  from 
the  bottle,  we  light  the  hydrogen  at  the  two  jets. 
At  one  it  burns  with  a  colorless  flame :  it  is  the 
flame  of  hydrogen  just  as  it  comes  from  the  gen- 
erating bottle.  The  other  flame  is  quite  bright ;  the 
hydrogen  which  has  passed  through  the  benzene  has 
become  charged  with  the  vapor  of  that  volatile  liquid, 
and  as  that  vapor,  containing  hydrogen  and  carbon, 
is  decomposed  by  the  heat  before  it  burns,  the  carbon  particles 
become  incandescent. 

When  the  flame  of  illuminating  gas  or  of  a  lamp  is  supplied 
with  oxygen  at  .the  inside,  the  particles  of  carbon  are  burned  in- 
stantly and  do  not  become  hot:  the  flame  then  gives  uo  light. 
This  is  the  case  in  the  Bunsen  burner  (Fig.  26),  in  which  the 
force  of  the  escaping  gas  draws  air  through 
holes  in  a  tube  surrounding  the  jet ;  the  air 
and  gas  mix  together,  and  all  the  carbon  is 
consumed  before  it  can  become  incandescent. 
We  then  have  a  flame  which  gives  great  heat, 
but  does  not  deposit  smoke  on  any  vessels 
which  we  may  heat  in  it. 

If  we  hold  a  piece  of  lime  in  the  flame  of 
the  oxyhydrogen  blow-pipe,  it  becomes  very 
hot  and  emits  a  brilliant  light.  This  is 
known  as  the  calcium  light.  In  the  Welsbach 
burner  the  lime  is  replaced  by  a  gauze  man- 
tle of  thorium  oxide,  the  heat  being  supplied 
by  a  non-luminous  Bunsen  flame. 

33.  Slow  Combustion. — All  the  examples  of  oxidation  which 
we   have  so  far  considered  are  said  to  be  cases  of  rapid  com- 


32  LESSONS   IN    CHEMISTRY. 

bustion :  they  take  place  with  the  production  of  intense  heat  and 
light.  Sometimes,  however,  there  is  no  bright  light,  no  high 
temperature,  and  yet  combustion  takes  place  as  certainly  as  before. 
A  piece  of  iron  which  rusts  by  exposure  to  damp  air  is  only  com- 
bining with  oxygen,  and  the  rust  is  a  compound  of  iron  with  the 
oxygen  and  moisture  of  the  atmosphere :  here  the  heat  of  chemi- 
cal union  is  developed  so  slowly  that  it  is  conducted  away  by  the 
air  and  surrounding  bodies,  and  the  iron  does  not  become  heated. 
Kespiration  is  a  slow  combustion.  The  warmth  of  our  bodies, 
and  all  our  animal  motions,  are  due  to  the  gradual  oxidation  of  the 
carbon  and  hydrogen  of  our  tissues.  At  every  breath  fresh  oxy- 
gen is  introduced  into  the  lungs,  where  it  is  absorbed  by  the  blood 
and  carried  through  the  arteries  to  the  most  remote  parts  of 
the  system ;  then,  when  all  the  oxygen  in  the  blood  is  used,  the 
water  and  carbon  dioxide  produced  by  the  combustion  are  carried 
through  the  veins  to  the  lungs,  and  thrown  out  with  the  exhaled 
airr  Animal  life  itself  depends  on  this  slow  oxidation  :  we  all 
know  how  quickly  any  animal  perishes  from  suffocation  when  the 
supply  of  air  is  entirely  cut  off.  The  muscles  of  our  bodies  con- 
tain no  force  except  that  which  is  produced  by  the  combustion  of 
their  own  substance.  Great  muscular  exertion  consequently  re- 
quires increased  oxidation,  and  we  quickly  become  fatigued  when 
we  are  obliged  to  burn  up  our  tissues  more  rapidly  than  they  are 
remade  from  our  food.  Also,  the  quantity  and  kind  of  food  re- 
quired depend  upon  the  amount  and  kind  of  work  which  we 
must  perform. 


LESSON    IV. 

COMPOSITION  OP    WATER.— CHEMICAL  LAWS    AND 
THEORIES. 

34.  Water  is  the  sole  product  of  the  combustion  of  hydrogen 
in  air  or  oxygen.  Its  composition,  that  is,  the  proportion  in 
which  the  hydrogen  and  oxygen  are  combined  together,  may  be 


COMPOSITION    OF    WATER.  33 

determined  by  analysis  and  by  synthesis.  Analysis  is  the  separa- 
tion and  weighing  of  the  constituents  of  a  compound ;  synthesis 
means  the  formation  of  a  substance  by  causing  its  elements  to 
unite  in  the  proper  proportion. 

35.  Electrolysis  of  Water. — Electrolysis  means  the  decom- 
position of  a  substance  by  an  electric  current.  For  the  decomposi- 
tion of  pure  water  an  enormously  strong  current  would  be  re- 
quired, and  because  we  do  not  desire  to  use  such  a  strong  current 
we  employ  dilute  sulphuric  acid :  the  final  result  is  the  same  as  if 
we  were  to  use  water,  the  sulphuric  acid  being  found  unchanged 
after  the  experiment.  Instead  of  using  the  acid,  we  might  make 
a  strong  solution  of  ordinary  salt ;  the  salt  would  make  the  water 
a  better  conductor  of  electricity.  We  introduce  the  dilute  sul- 
phuric acid  (about  five  parts  of  water  to  one  of  acid)  into  a  vessel 
through  a  hole  in  the  bottom  of  which  are  cemented  two  wires, 
the  inner  ends  of  each  being  soldered  to  a  little  plate  of  thin  plat- 
inum. We  fill  two  small  test-tubes  with  water,  and,  closing  the 
mouths  with  the  fingers,  invert  one  over  each  of  these  plates  :  we 
now  connect  the  ends  of  the  wires  with  the  poles  of  a  voltaic  bat- 
tery (Fig.  27).  Little  bubbles  of  gas  at  once  begin  to  rise  in  the 
tubes,  and  as  soon  as 
the  quantities  of  gas  col- 
lected are  large  enough 
to  allow  us  to  notice  the 
volume  of  each,  we  see 
that  in  one  of  the  tubes 
there  is  twice  as  much 
as  iu  the  other.  When 
that  tube  is  filled,  we 
raise  it  carefully,  and 
the  introduction  of  a 

lighted  match  will  con- 

FIG.  27. 
vmce  us  that  the  gas  is 

hydrogen.  When  we  raise  the  other  tube,  keeping  the  end  closed 
with  the  thumb,  until  we  are  ready  to  push  into  it  a  match-stick 
bearing  a  spark,  the  kindling  of  the  spark  into  flame  shows  us 

3 


34 


LESSONS    IN    CHEMISTRY. 


that  the  second  gas  is  oxygen.     Water  is  then  composed  of  two 

volumes  of  hydrogen  combined  with  one  volume  of  oxygen. 
36.  We  have  seen  that  the  density  of  hydrogen  compared  to 

air  is  0.0695,  and  that  the  density  of  oxygen  is  1.1056.    A  given 

volume  of  oxygen  must  then  be 

1.1056  -r-  0.0695  =  16  (a  very  little  less), 

sixteen  times  as  heavy  as  an  equal  volume  of  hydrogen.  As  we 
have  two  volumes  of  hydrogen  and  only  one  of  oxygen, 
the  oxygen  in  water  must  weigh  eight  times  as  much  as 
the  hydrogen. 

37.  Eudiometric  Synthesis  of  Water. — A  eudio- 
meter is  a  graduated  strong  glass  tube,  closed  at  one  end 
near  which  two  thin  platinum  wires  are  soldered  into 
the  glass  on  opposite  sides ;  an  electric  spark  may  be 
passed  between  the  wires  on  the  inside  of  the  tube 
(Fig.  28).  If  we  fill  such  a  tube  with  mercury,  and, 
after  inverting  it  in  a  vessel  of  mercury,  pass  into  it 
some  hydrogen,  and  then  half  as  much  oxygen,  an 
electric  spark  will  cause  the  gases  to  combine ;  after  the 
little  explosion  which  takes  place  in  the  tube,  the  water 
which  is  formed  is  condensed  in  minute  drops  in  the 
cold  tube,  and  the  atmospheric  pressure  forces  the  mer- 
cury up,  filling  the  tube  completely.  Here,  again,  we 
see  that  water  is  composed  of  two  volumes  of  hydrogen 
combined  with  one  volume  of  oxygen. 


FIG.  28  FIG.  29. 

38.  Synthesis  by  Weight.— We  may  make  the  synthesis  of 


CHEMICAL   LAWS    AND   THEORIES.  35 

water  by  a  very  instructive  method  which  was  first  adopted  by  the 
French  chemist  Dumas.  We  prepare  hydrogen  from  sulphuric  acid 
and  zinc  in  the  ordinary  manner,  and  thoroughly  dry  it  by  passage 
through  a  tube  (A)  containing  little  pieces  of  pumice-stone  wet 
with  strong  sulphuric  acid  (Fig.  29).  We  then  cause  it  to  pass 
through  a  tube  containing  some  cupric  oxide  (B),  a  black  com- 
pound of  copper  and  oxygen,  and  this  tube  is  connected  with  a 
U-shaped  tube  (C)  filled  with  pumice-stone  also  moistened  with 
strong  sulphuric  acid.  The  U  tube  is  placed  in  a  vessel  contain- 
ing some  broken  ice.  Before  connecting  our  tubes  together,  we 
have  carefully  weighed  that  holding  the  cupric  oxide,  and  the  last 
U  tube  with  its  contents.  When  this  whole  apparatus  is  filled 
with  the  hydrogen  coming  from  the  bottle,  we  heat  the  cupric 
oxide  by  a  spirit-lamp,  and  when  it  becomes  hot  the  hydrogen  gas 
takes  away  the  oxygen  from  the  copper.  Steam  is  formed  and  is 
condensed  in  the  U  tube  (C).  When  the  color  of  the  cupric  oxide 
has  entirely  changed  to  red,  we  warm  the  whole  length  of  the 
tube  containing  it,  in  order  to  drive  all  of  the  water  over  into  the 
U  tube :  we  allow  our  apparatus  to  cool,  take  it  apart,  and  again 
weigh  the  tubes  of  which  we  had  determined  the  weight  before 
the  experiment.  The  copper  which  is  left  in  the  first  will  weigh 
just  as  much  less  than  the  cupric  oxide  as  the  latter  has  lost  oxy- 
gen. The  increased  weight  of  the  U  tube  (C)  will  be  the  weight 
of  the  water  formed,  and  by  subtracting  from  this  weight  the 
weight  of  the  oxygen,  we  will  have  the  weight  of  the  hydrogen 
contained  in  that  water.  We  find  that  there  is  almost  exactly 
eight  times  as  much  oxygen  as  hydrogen.  In  very  accurate  ex- 
periments we  would  perfectly  purify  our  hydrogen  and  adopt  all 
possible  precautions  that  no  vapor  of  water  might  escape  from  the 
tube  C. 

CHEMICAL   LAWS  AND   THEORIES. 

39.  No  matter  by  what  process  water  may  be  formed,  no  matter 
by  what  process  its  composition  may  be  determined,  it  is  always 
found  to  contain  the  same  proportions  of  oxygen  and  hydrogen ; 
never  more  nor  less  than  eight  (7.94  exactly)  parts  by  weight  of 


36  LESSONS    IN    CHEMISTRY. 

the  first  for  one  of  the  second.  If  we  try  to  combine  the  gases 
in  other  proportions,  the  -excess  of  the  one  or  other,  out  of  the 
proportion  one  to  eight,  will  be  left  uncombined.  The  analysis 
of  all  known  substances  has  shown  a  similar  constancy  of  corn- 
position,  a  constancy  which  is  expressed  in  the  following 

40.  LAW  OF   DEFINITE   PROPORTIONS:    The  proportion  by 
weight  in  which  the  elements  exist  in  any  compound,  is  invaria- 
ble.    This  is  generally  called  Dalton's  first  law. 

41.  We  have  already  found  that  the   proportions  by  volume 
according  to  which  oxygen  and  hydrogen  unite  are  one  to  two. 
This  is  a  simple  relation  of  volumes.     Experiments  with  other 
gases  will  in  time   show  us  that  when   gases  combine,  there  is 
always  some  such  simple  relation  between  the  volumes  of  the  gases 
that  enter  into  combination.     Thus, 

One  volume  of  hydrogen  combines  with  exactly  one  volume  of  chlorine. 
Two  volumes  of  hydrogen  combine  with  exactly  one  volume  of  oxygen. 
Three  volumes  of  hydrogen  combine  with  exactly  one  volume  of  nitrogen. 
Two  volumes  of  nitrogen  combine  with  exactly  one  volume  of  oxygen. 

We  might  find  many  more  such  examples,  and  the  statement 
of  these  facts  constitutes 

GAY-LUSSAC'S  FIRST  LAW  :  there  is  a  simple  relation  between 
the  volumes  of  gases  which  combine. 

42.  Let  us  study  the  volume  of  the  compound 
formed  when  that  compound  is  in  the  same  con- 
dition as  the  original  elements  ;  that  is,  the  gaseous 
state. 

By  grinding  together  with  emery,  we  have 
accurately  fitted  together  the  necks  of  two  glass 
bottles  that  have  exactly  the  same  capacity  (Fig. 
30).  We  fill  the  lower  one  with  perfectly  dry 
chlorine  gas  (§  71),  and  the  upper  with  dry  hydro- 
gen, and  then  hermetically  join  them  together  by 
the  ground  joint.  All  of  this  must  be  done  in  a 
room  lighted  only  by  a  candle  or  small  gas-flame. 
We  now  allow  the  apparatus  to  stand  for  a  day  in 

FIG.  30.        a  room  wjjere  tne  sunlight  may  not  shine  on  it 


COMPOSITION    OF    WATER. 


37 


directly.  The  gases  will  slowly  combine,  and  the  yellowish  color  of 
the  chlorine  will  disappear.  When  we  open  the  bottles  under  the 
surface  of  mercury,  we  will  find  that  no  gas  escapes  from  them,  and 
no  mercury  enters.  The  gas  hydrochloric  acid  has  been  formed,  and 

Two  volumes  of  hydrochloric  acid  must  contain  j  ODe  volume  °f  hydr°gen  and 

I  one  volume  of  chlorine. 

Over  the  open  end  of  a  eudiometer  we  have  passed  a  piece  of 
strong  rubber  tubing,  to  the  other  end  of  which  is  attached  a 
straight  glass  tube  about  the  size  and  length  of  the  eudiometer ; 
the  rubber  tube  is  firmly  tied  at  each  joint.  We  fill  our  apparatus 
with  mercury,  place  it  vertically  in  the  mer- 
cury trough,  and  introduce  five  cubic  centi- 
metres of  oxygen  and  ten  cubic  centimetres 
of  hydrogen.  We  now  close  the  end  of  the 
tube  with  the  finger,  lift  it  from  the  trough, 
and,  after  bringing  the  two  tubes  parallel  to 
each  other,  clamp  them  in  that  position  in  a 
stand  (Fig.  31).  We  have  tightly  fitted  a 
perforated  cork  around  the  lower  end  of  the 
eudiometer,  and  on  this  cork  we  now  as  tightly 
fit  the  lower  end  of  a  wide  glass  tube,  which 
we  slip  over  the  eudiometer,  whose  wires  we 
have  connected  with  long  copper  wires  that 
pass  out  at  the  upper  end  of  the  wide  tube. 
We  now  fill  the  wide  tube  with  perfectly  clear 
oil  (lard  oil  or  sweet  oil)  heated  to  130°  ;  we 
mljust  the  mercury  at  the  same  level  in  the 
two  tubes,  and,  after  carefully  reading  the  vol- 
ume occupied  by  the  mixed  gases,  we  pass  an  electric  spark  in  the 
eudiometer.  The  gases  of  course  combine :  steam  is  formed,  but 
does  not  condense,  because  the  eudiometer  is  heated.  On  again 
making  the  mercury  levels  the  same,  and  examining  the  volume 
of  this  steam,  we  find  that  it  is  only  two-thirds  as  great  as  that 
of  the  mixed  gases  :  in  other  words, 


FIG.  31. 


Two  volumes  of  steam  contain 


two  volumes  of  hydrogen  and 
one  volume  of  oxygen. 


38  LESSONS   IN    CHEMISTRY. 

Ammonia  gas  is  a  compound  of  hydrogen  and  nitrogen,  and  its 
analysis  proves  that  two  volumes  of  the  gas  may  be  decomposed 
into  one  volume  of  nitrogen  and  three  volumes  of  hydrogen. 

On  comparing  these  results,  we  find  that 

Two  volumes  of  hydrochloric  acid  contain  one  volume  of  hydrogen  and  one 
volume  of  chlorine. 

Two  volumes  of  vapor  of  water  contain  two  volumes  of  hydrogen  and  one  vol- 
ume of  oxygen. 

Two  volumes  of  ammonia  contain  three  volumes  of  hydrogen  and  one  volume 
of  nitrogen. 

We  see  that  not  only  is  there  a  simple  relation  between  the 
volumes  of  gases  which  combine,  but,  as  is  expressed  in 

GAY-LussAc's  SECOND  LAW,  there  is  a  simple  relation  between 
the  volume  of  a  compound  gas  and  the  sum  of  the  volumes  of  the 
gases  which  form  that  compound. 


LESSON    V. 
CHEMICAL  LAWS   AND   THEORIES    (Continued). 

43.  Equivalent  Combining  Proportions. — Careful  analysis 
of  hydrochloric  acid  has  shown  that  it  is  composed  of  35.5  parts 
by  weight  of  chlorine  combined  with  one  part  by  weight  of  hydro- 
gen. Chlorine  combines  with  mercury,  forming  a  compound 
called  mercuric  chloride  or  corrosive  sublimate ;  this  compound 
contains  for  every  35.5  parts  of  chlorine,  exactly  100  parts  of 
mercury.  We  dissolve  135.5  grammes  of  mercuric  chloride  in 
water,  and  put  some  zinc  into  the  solution :  the  chlorine  has  a 
stronger  affinity  for  the  zinc  than  for  the  mercury ;  it  conse- 
quently combines  with  the  zinc,  forming  zinc  chloride,  which  re- 
mains in  the  solution,  while  mercury  separates.  If  we  wait  until 
all  the  35.5  grammes  of  chlorine  which  were  combined  with  100 
grammes  of  mercury  have  united  with  the  zinc,  and  then  deter- 
mine the  quantity  of  zinc  which  is  required  to  combine  with  that 
quantity  of  chlorine,  we  would  find  that  the  zinc  chloride  formed 


CHEMICAL  LAWS  AND  THEORIES.  39 

weighs  68.25  grammes :  that  is,  32.75  (68.25  —  35.5)  grammes 
of  zinc  combine  with  35.5  grammes  of  chlorine.  Consequently,  as 
far  as  combining  with  chlorine  is  concerned,  32.75  parts  of  zinc 
have  just  as  much  power  as  100  parts  of  mercury. 

Oxygen  combines  with  mercury  and  with  hydrogen :  it  com- 
bines also  with  zinc  and  with  chlorine.  Analysis  of  the  com- 
pounds so  formed  shows  that  35.5  parts  of  chlorine  will  combine 
with  8  parts  of  oxygen,  and  that  8  parts  of  oxygen  will  combine 
with  32.75  parts  of  zinc  or  with  100  of  mercury.  We  have 
already  seen  (§  36)  that  8  parts  of  oxygen  combine  with  one  part 
of  hydrogen.  These  numbers  must  then  express  the  relations 
between  the  combining  quantities  of  the  corresponding  elements. 
Thousands  of  analyses  have  shown  that  similar  equivalent  propor- 
tions exist  for  all  of  the  elements.  The  combining  proportions  so 
found  must  bear  simple  relations  to  the  relative  weights  of  the 
atoms ;  for  if  atoms  have  a  real  existence,  chemical  combination 
must  result  from  the  union  of  one,  two,  or  more  atoms  of  one 
element  with  one,  two,  or  more  atoms  of  another;  and,  since 
combination  is  in  definite  proportions,  the  same  substance  must 
always  result  from  the  union  of  the  same  kind  of  atoms  in  the 
same  proportion. 

44.  If  it  be  possible  to  determine  the  relative  weights  of  the 
molecules,  compared  with  any  unit,  and  to  arrive  at  definite  con- 
clusions as  to  the  number  of  atoms  these  molecules  contain,  then 
we  can  determine  the  relative  weights  of  the  atoms.     Some  new 
considerations  will  enable  us  to  make  such  determinations. 

LAW  OF  AVOGADRO  AND  AMPERE.— ATOMIC  THEORY. 

45,  Different  solid  and  liquid  substances  expand  in  very  dif- 
ferent degrees  by  the  action  of  the  same   temperature.     Gases, 
however,  all  expand  alike.     If  at  the  same  pressure  we  raise  or 
lower  the  temperature  of  equal  volumes  of  different  gases  through 
the  same  number  of  degrees,  we  find  that  they  all  expand  or  con- 
tract precisely  the  same  proportion  of  the  volume.     If  expansion 
be  separation  of  molecules  from  one  another  (§8),  it  follows  that 
equal  volumes  of  gases,  measured  at  the  same  temperature  and 


40  LESSONS    IN    CHEMISTRY. 

pressure,  contain  the  same  number  of  molecules.  This  hypothesis, 
proposed  by  Avogadro  and  Ampere,  is  true  if  there  be  such  things 
as  molecules,  and  if  there  be  no  molecules  we  can  explain  no 
chemical  phenomena. 

46.  If  equal  volumes  of  gases  contain  the  same  number  of 
molecules,  the  relative  weights  of  those  equal  volumes  must  also 
express  the  relative  weights  of  the  molecules.  The  relative  weights 
are  the  densities,  and  these  densities  are  usually  calculated  to  ex- 
press the  relation  between  the  weight  of  the  gas  and  that  of  an 
equal  volume  of  air,  which  is  taken  as  unity.     Since  hydrogen  is 
the  lightest  gas,  its  molecule  must  have  the  least  weight :    the 
density  of  oxygen  is  sixteen  times  as  great  as  that  of  hydrogen,  and 
the  molecule  of  oxygen  must  be  sixteen  times  as  heavy  as  that  of 
hydrogen.     Because  of  the  lightness  of  the  molecule  of  hydrogen, 
ohemists  have  chosen  that  molecule  as  the  standard  of  comparison 
for  other  molecules, — i.e.,  the  molecular  weights  are  referred  to  it. 
The  density  of  hydrogen  compared  to  air  being  0.0695,  the  air 
is  14.39  times  as  heavy  as  hydrogen :  consequently,  if  we  know 
the  density  of  a  gas  compared  to  air,  we  may  easily  calculate 
its  density  compared  to  hydrogen  by  multiplying  the  first'  by 
14.39.      Thus,  the  density  of  vapor  of  water  compared  to  air 
is  0.06213,  compared  to  hydrogen  it  is  0.06213  X  14.388  = 
8.94.     The  molecule  of  water  is  therefore  about  nine  times  as 
heavy  as  that  of  hydrogen. 

47.  Let  us  see  now  whether  we  can  determine  the  relations 
between  the  weight  of  any  atom  and  that  of  a  molecule  of  hydro- 
gen.    According  to  the  law  of  Avogadro,  the  oxygen  molecule  is 
sixteen  times  heavier  than  the  hydrogen  molecule.     One  volume 
of  oxygen  combines  with  two  volumes  of  hydrogen,  and  the  result 
is  two  volumes  of  water  vapor.     How  many  atoms  of  hydrogen 
are  contained  in  one  molecule  of  this  vapor?     To  answer  this 
question  we  must  remember  that  two  volumes  of  hydrochloric 
acid,  containing  just  as  many  molecules  as  two  volumes  of  steam, 
contain  only  half  as  much  hydrogen  as  the  two  volumes  of  steam 
(§  41).     If,  then,  the  molecule  of  hydrochloric  acid  contains  one 
atom  of  hydrogen  (and  it  cannot  contain  less)  the  molecule  of 
water  vapor  must  contain  two.     And  if  the  molecule  of  water 


CHEMICAL    LAWS    AND    THEORIES.  41 

vapor  contains  two  atoms  of  hydrogen,  the  weight  of  this  mole- 
cule must  be  eighteen  times  as  great  as  that  of  an  atom  of  hydro- 
gen, for  water  contains  oxygen  and  hydrogen  in  the  ratio  8  :  1 
=  16:2.  Then,  if  a  molecule  of  water  contains  hut  one  atom 
of  oxygen,  and  there  is  no  reason  to  believe  that  it  contains 
more  than  one,  the  oxygen  atom  must  weigh  sixteen  times  as 
much  as  that  of  hydrogen. 

48.  Now  we  may  apply  our  theory  to  the  facts  already  studied. 

Two  volumes  of  hydrogen  represent  two  atoms,  each  of  which 
weighs  one :  two  volumes  of  oxygen  represent  two  atoms,  each  of 
which  weighs  sixteen.  Water  is  formed  by  the  union  of  two 
atoms  of  hydrogen  and  one  atom  of  oxygen,  and  a  molecule  of 
water  weighs  eighteen  times  as  much  as  an  atom  of  hydrogen. 

A  molecule  of  hydrochloric  acid  contains  one  atom  of  hydrogen 
and  one  atom  of  chlorine,  and  this  molecule  weighs  36.5  if  one 
atom  of  hydrogen  weighs  1. 

A  molecule  of  ammonia  contains  one  atom  of  nitrogen  (weigh- 
ing 14)  and  three  atoms  of  hydrogen,  and  is  17  times  as  heavy  as 
an  atom  of  hydrogen. 

But  the  density  of  water  compared  to  hydrogen  is  9 ;  that  of 
hydrochloric  acid,  18.25,  and  that  of  ammonia,  8.5.  We  see  then 
that  if  an  atom  of  hydrogen  occupies  one  volume  and  weighs  one, 
the  molecule  of  any  substance  in  a  state  of  gas  or  vapor  must 
occupy  twice  as  much  volume  as  one  atom  of  hydrogen,  and  the 
weight  of  the  molecule  will  be  expressed  by  twice  the  density  of  the 
gas  or  vapor  referred  to  hydrogen.  In  other  words,  the  standard 
of  molecular  weight  is  2,  since  there  are  two  atoms  in  the  mole- 
cule of  hydrogen. 

Different  methods  are  employed  for  determining  the  atomic 
weights  of  the  elements.  At  this  point  we  need  only  understand 
that  if  the  element  be  gaseous  or  volatile,  and  if  we  have  reason  to 
believe  that  its  molecule  contains  two  atoms,  then,  since  the  mole- 
cule of  hydrogen  consists  of  two  atoms,  and  equal  volumes  of 
gases  contain  equal  numbers  of  molecules,  the  same  figures  which 
express  the  density  of  the  gas  compared  to  hydrogen,  will  express 
also  the  atomic  weight. 


42  LESSONS    IN    CHEMISTRY. 

This  atomic  theory,  which  has  been  slowly  developed  during  the 
present  century,  furnishes  an  intelligible  explanation  of  chemical 
phenomena.  New  discoveries  are  continually  bringing  new  facts  to 
its  support,  and,  though  it  may  be  modified  by  the  results  of  future 
researches,  its  principal  features  will  probably  remain  undisturbed. 

CHEMICAL  NOTATION. 

49.  In  order  that  the  composition  of  a  substance,  that  is,  the 
number  and  kinds  of  atoms  in  its  molecules,  may  be  understood  at 
a  glance,  we  employ  a  special  method  of  representing  elements  and 
compounds.     The  first  letter,  or  the  first  and  another  letter,  of 
the  name  of  an  element,  is  used  to  express  one  atom  of  that  ele- 
ment.    Thus,  H  means  one  atom  of  hydrogen  ;  O,  one  of  oxygen  ; 
S,  one  of  sulphur ;  C,  one  of  carbon,  and  Ca,  one  of  calcium. 
These  are  called  the  symbols  of  the  elements.     More  than  one 
atom  is  expressed  by  a  little  figure  placed  to  the  right  of  the 
symbol,  slightly  above  or  below  its  central  line  ;  H2  or  H2  (read 
H  two)  means  two  atoms  of  hydrogen  ;  0*  represents  four  atoms 
of  oxygen.     Compounds  are  then  written  so  that  the  symbols 
entering  into  the  formula  express  the  number  and  kind  of  atoms 
in  a  molecule.    H20  means  a  molecule  of  water,  composed  of  two 
atoms  of  hydrogen  and  one  of  oxygen  :  H2S04  means  a  molecule 
of  sulphuric  acid,  containing  two  atoms  of  hydrogen,  one  of  sul- 
phur, and  four  of  oxygen.     To  express  any  number  of  molecules 
we  use  an  ordinary  figure  placed  to  the  left  of  the  formula ;  thus, 
2HC1  means  two  molecules  of  hydrochloric  acid,  each  of  which 
contains  one  atom  of  hydrogen  and  one  of  chlorine. 

50.  We  may  now  study  the  molecular  changes  which  have  oc- 
curred in  the  chemical  phenomena  that  we  have  already  observed. 
In  the  decomposition  of  water  by  sodium,  one  atom  of  hydrogen 
in  each  molecule  of  water  is  replaced  by  sodium,  and  when  a  mole- 
cule of  hydrogen  is  set  free,  two  molecules  of  a  compound  called 
sodium  hydroxide  are  formed.     We  represent  the  change  thus : 

2H2Q  +         Na2        =         2NaOH         +  H2 

2  molecules  of  2  atoms  of  2  molecules  of  1  molecule  of 

water.  sodium.         sodium  hydroxide.          hydrogen. 

This  chemical  equation  expresses  the  changes  which  take  place 


CHEMICAL   LAWS   AND   THEORIES.  43 

in  the  chemical  reaction.  As  the  symbol  for  each  atom  means  a 
definite  quantity  of  matter,  and  as  there  can  be  no  change  in  the 
quantity  of  matter  during  the  reaction,  there  must  be  as  many 
atoms  represented  in  one  member  of  the  equation  as  in  the  other. 
When  we  know  what  is  formed  by  the  reaction  of  certain  mole- 
cules, our  equation  will  enable  us  to  calculate  the  quantities  of  the 
substances.  The  weight  of  one  atom  of  sodium  being  23 ;  one 
atom  of  hydrogen,  1  ;  and  one  atom  of  oxygen,  16,  we  find  that 
46  grammes  of  sodium  will  yield  2  grammes  of  hydrogen,  and  80 
grammes  of  sodium  hydroxide. 

2HOH      +       Na2    =       2NaOH        +    H* 

*  2  (1  +  16  +  1)        23  +  23        2(23  H-  16  +  1)        1  +  1. 

We  can  calculate  the  volume  of  the  hydrogen  at  0°,  from  its 
weight  (§  19),  and  we  can  so  estimate  the  weight  and  volume 
of  hydrogen  which  will  be  set  free  by  any  given  quantity  of 
sodium.  Chemical  formulae  and  equations  thus  represent  more 
than  mere  theory ;  they  exactly  express  the  combining  propor- 
tions. 

The  action  of  sulphuric  acid  on  zinc,  which  yields  zinc  sulphate 
and  hydrogen,  is  written 

Zn  +        R2S04        =        ZnSO*        +  H2 
Sulphuric  acid.        Zinc  sulphate. 

Of  course  we  must  know  by  experiment  what  is  formed  in  a 
reaction,  before  we  can  write  the  chemical  equation  ;  we  must  also 
know  by  analysis  the  proportions  of  the  elements  in  any  compound 
before  we  can  write  a  formula  which  we  believe  to  express  the 
atoms  in  its  molecule. 

The  decomposition  of  potassium  chlorate  by  heat  (§  26)  is 

2KC103  2KC1  +     302 

Potassium  chlorate,        Potassium  chloride,        Oxygen, 
2  molecules.  2  molecules.  3  molecules. 

That  of  mercuric  oxide,  in  the  same  manner,  is 
2HgO       =     2Hg      +  O2 

Mercuric  oxide.        Mercury. 

The  reaction  of  hydrogen  with  cupric  oxide,  which  enabled  us 
to  make  the  synthesis  of  water,  is  written 

CuO       +  H2  =  H2Q  +      Cu 

Cupric  oxide.  Copper. 


44 


LESSONS    IN   CHEMISTRY. 


51.  The  following  table  gives  the  names  and  symbols  of  the 
elements  which  are  at  present  known,  and  the  weights  of  the 
atoms  compared  to  the  weight  of  an  atom  of  hydrogen.  Some  of 
these  atomic  weights  might  be  more  exactly  expressed ;  an  atom 
of  oxygen  is  15.88  times  as  heavy  as  that  of  hydrogen ;  the  exact 
atomic  weight  of  nitrogen  is  13.93 ;  but  these  numbers  are  so 
nearly  16  and  14,  that  for  memory's  sake  it  is  preferable  to  use 
the  nearest  whole  numbers. 


NAMES  OF  THE  ELE- 
MENTS. 

Symbols. 

Atomic 
Weights. 

NAMES  OF  THE  ELE- 
MENTS. 

Symbols. 

Atomic 
Weights. 

Aluminium    . 

Al 

27 

Metargon      .... 

AM 

40(?) 

Antimony  (stibium) 

Sb 

120 

Molybdenum        .    . 

Mo 

96 

Argon  

A 

40  (^) 

Neodymium  • 

Nd 

139.4 

Arsenic     .... 

As 

IV  ^.   j 

75 

Neon     

Ne 

22  (f) 

Barium     .... 

Ba 

137 

Nickel       

Ni 

59 

Bismuth    .... 

Bi 

208 

Niobium   ..... 

Nb 

94 

Boron  

B 

11 

Nitrogen 

N 

14 

Bromine    .... 

Br 

80 

Osmium    .    .      .  „    . 

Os 

190 

Cadmium  .... 

Cd 

'  112 

Oxygen     

0 

16 

Caesium     .... 

Cs 

133 

Palladium    .... 

Pd 

106.6 

Calcium    .... 

Ca 

40 

Phosphorus      .    .    . 

P 

31 

Carbon      .     . 

C 

12 

Platinum      .... 

Pt 

193.5 

Cerium      .... 

Ce 

140 

Potassium  (kalium) 

K 

39.1 

Chlorine    .... 

Cl 

35.5 

Praseodymium    .    . 

Pr 

142.4 

Chromium     .     .     . 

Cr 

52.5 

Rhodium      .... 

Rh 

102.2 

Cobalt  

Co 

59 

Rubidium     .... 

Rb 

85.2 

Copper      .... 

Cu 

63.1 

Ruthenium       .    .    . 

Ru 

100.9 

Erbium     .... 

Er 

166 

Scandium     .... 

Sc 

44 

Fluorine  .... 

F 

19 

Selenium  

Se 

79.5 

Gallium    .... 

Ga 

69 

Silicon           .... 

Si 

28 

Germanium  .     .     . 

Ge 

72 

Silver  (argentuin)  . 

Ag 

108 

Glucinum 

Gl 

9 

Sodium  (natrium)  . 

Na 

23 

Gold  (aurum)    . 

Au 

195.7 

Strontium     .... 

Sr 

87.5 

Helium     .... 

He 

4(?) 

Sulphur    

s 

32 

Holmium  .... 

Ho 

162  (?) 

Tantalum     .    .  y  .; 

Ta 

182 

Hydrogen 

H 

1 

Tellurium     .... 

Te 

125 

Indium     .... 

In 

113.4 

Thallium  

Tl 

204 

Iodine  

I 

127 

Thorium 

Th 

234 

Iridium     .... 

Ir 

192 

Tin  (stannum)     .    . 

Sn 

118 

Iron  (ferruin)     .     . 

Fe 

56 

Titanium      .... 

Ti 

48 

Krypton  .... 

Kr 

80(?) 

Thulium   

Tu 

170.4  (?) 

Lanthanum  . 

La 

139 

Tungsten     (wolf'ra- 

Lead  (plumbum)    . 

Pb 

207 

mium)   

W 

184 

Lithium    .... 

Li 

7 

Uranium  

U 

238 

Magnesium   .     .     . 

Mg 

24 

Vanadium    .... 

V 

51 

Manganese    .     .     . 

Mn 

55 

Ytterbium    .... 

Yb 

173 

Mercury     (hydrar- 

Yttrium     

Y 

89 

gyrum)  .     .     . 

Hg 

200 

Zinc  

Zn 

65 

Zirconium    .... 

Zr 

90 

PROPERTIES    OF    WATER.  45 


LESSON     VI. 

PROPERTIES    OF   WATER.— POTABLE   AND   MINERAL 
WATERS. 

52.  Pure  water  is  not  met  with  in  nature.  When  we  desire  it, 
it  must  be  prepared  by  distilling  water ;  that  is,  boiling  it  in  a  re- 
tort, and  condensing  the  steam.  We  usually  conduct  this  distilla- 
tion in  tin-lined  copper  retorts.  For  most  of  the  distillations  in 
the  laboratory  we  employ  a  flask  or  retort,  connected  with  a  long 
tube  which  is  surrounded  by  a  wider  tube,  and  a  stream  of  cold 


FIG.  32. 

water  continually  flows  through  the  space  between  the  two  tubes 
in  this  condenser,  as  we  call  it  (Fig.  32). 

Pure  water  has  neither  taste  nor  odor ;  although  it  is  colorless 
in  small  quantity,  it  has  a  deep-blue  color  when  in  large  masses. 
It  solidifies  when  sufficiently  cooled,  and,  since  it  is  always  con- 
verted into  ice  at  the  same  temperature,  that  temperature  is  taken 
as  0°  in  the  centigrade  thermometer  scale  which  we  use  in  the 
laboratory. 

53.  The  temperature  of  water  does  not  change  while  it  is  freez- 
ing, and  that  of  ice  does  not  change  while  it  is  melting.  This  is 
because  all  the  heat  which  is  communicated  to  ice  during  its 
melting  is  required  to  produce  the  change  of  state ;  indeed,  one 


46  LESSONS    IN   CHEMISTRY. 

kilogramme  of  ice  at  0°  requires  as  much  heat  to  melt  it  as  would 
raise  79  kilogrammes  of  water  from  0°  to  1°,  or  one  kilogramme 
from  0°  to  79°,  and  yet  the  water  from  the  melted  ice  still  has  a 
temperature  of  0°.  Ice  is  crystallized ;  it  consists  of  a  great  many 
little  six-sided  pyramids  dovetailed  together.  We  can  notice  the 


FIG.  33. 

crystalline  form  of  water  by  examining  some  snow-flakes  that  have 
fallen  on  black  cloth  (Fig.  33). 

During  the  cooling  of  water,  it  contracts  in  volume  until  its 
temperature  reaches  4°  ;  it  then  begins  to  expand,  and  on  freezing 
expands  considerably.  Ice  is  only  0.93  as  heavy  as  water  at  4°. 
Strong  vessels  are  broken  by  the  freezing  of  water  in  them,  and 
it  is  the  same  expansion  which  kills  delicate  plants  by  frost,  for 
the  ice  formed  in  them  tears  apart  the  fibres  and  destroys  the  sap- 
vessels.  Since  it  is  easy  everywhere  to  obtain  water  at  its  point 
of  maximum  density,  that  is,  4°,  this  density  has  been  chosen  as 
the  unit  of  density  or  specific  gravity  for  liquids  and  solids.  It 
is  also  at  this  temperature  that  one  litre  of  water  weighs  one  kilo- 
gramme. 

Water  and  ice  continually  emit  invisible  vapor,  but  water  does 
not  begin  to  boil  until  its  tension  of  vapor  *  is  equal  to  the  at- 
mospheric pressure.  We  consider  that  the  normal  atmospheric 
pressure  is  equal  to  that  of  a  column  of  mercury  760  millimetres 

*  The  tension  of  vapor  of  a  liquid  at  any  temperature  is  measured  by  the 
decrease  in  the  height  of  the  mercury  in  a  barometer-tube,  up  into  which  the 
liquid  is  passed  in  small  quantities  until  no  more  of  it  changes  into  vapor. 
The  number  of  millimetres  through  which  the  level  of  the  mercury  has  then 
fallen,  expresses  the  tension  of  the  vapor. 


PROPERTIES    OF    WATER.  47 

in  height,  and  under  this  pressure  the  boiling  point  of  water  is 
selected  as  the  100°  point  of  the  centigrade  thermometer. 

While  water  is  boiling,  its  temperature  does  not  rise  :  after  it 
has  reached  the  boiling  point,  all  the  heat  passes  into  the  steam, 
where  it  is  required  to  hold  apart  the  molecules.  To  convert  one 
kilogramme  of  water  at  100°  into  steam  requires  as  much  heat 
as  would  raise  the  temperature  of  537  kilogrammes  of  water 
from  0°  to  1°,  or  5.37  kilogrammes  from  0°  to  100°.  The 
conversion  of  water  into  steam  expands  it  1696  times:  that  is, 
one  litre  of  water  will  yield  1696  litres  of  steam  at  100°. 

54.  Chemical  Properties. — We  have  seen  that  water  is  de- 
composed by  an  electric  current :  it  is  also  decomposed  by  very 
high  temperatures  (1200°).     We  will  find  that  it  enters  into 
many  chemical  reactions,  in  some  of  which  it  is  decomposed  and 
part  of  its  hydrogen  set  free,  as  in  the  experiment  with  sodium 
(§  3).     In  other  cases  both  the  oxygen  and  hydrogen  atoms  are 
taken  into  new  combinations.     Water  forms  a  large  proportion  of 
animal  and  vegetable  tissues. 

Water  dissolves  many  substances,  solid,  liquid,  and  gaseous. 
We  all  know  that  salt,  sugar,  and  alum  will  dissolve  in  water,  be- 
coming for  the  time  part  of  the  liquid.  We  immerse  the  bulb  of 
a  thermometer  in  a  vessel  of  water,  into  which  we  throw  some 
ammonium  nitrate,  and  stir  the  liquid :  at  once  the  thermometer 
indicates  a  lower  temperature.  When  solids  dissolve  in  water, 
cold  is  produced,  because  the  heat  required  to  separate  the  mole- 
cules of  the  solid  must  be  taken  from  the  water.  On  the  con- 
trary, when  gases  dissolve  in  water,  the  liquid  becomes  warmer, 
because  the  heat  no  longer  required  to  hold  apart  the  molecules 
of  the  gas  can  now  raise  the  temperature. 

55.  Water  exerts  a  very  curious  action  on  some  substances 
We  take  some  large  blue  crystals  of  cupric  sulphate  and  hea, 
them  on  a  piece  of  tin  over  a  lamp.     We  see  that  they  gradually 
become  white,  and  crumble  into  a  powder.     We  throw  some  of 
this  powder  into  water,  and  the  water  becomes  blue ;  cupric  sul- 
phate pan  only  exist  in  crystals  when  it  is  combined  with  water, 
and  fr  is  blue  only  when  combined  with  water.     In  the  same 


48  LESSONS    IN    CHEMISTRY. 

manner  water  is  necessary  to  the  crystalline  form,  and  often  to 
the  color,  of  many  substances,  and  when  combined  in  this  way  is 
called  water  of  crystallization.  Water  of  crystallization  is  chem- 
ically combined  in  the  crystals,  for  it  is  always  in  definite  propor- 
tions. In  a  piece  of  crystallized  cupric  sulphate  there  are  five 
molecules  of  water  for  every  molecule  of  copper  sulphate. 

56.  NATURAL  WATER. — As  it  occurs  naturally,  water  always 
contains  foreign  matters  suspended  or  dissolved  in  it.     These  sub- 
stances are  derived  from  the  air  through  which  the  rain  falls,  or 
from  the  soil  over  which  the  water  flows. 

57.  According  to  the  kind  and  quantity  of  these  matters 
present,  the  water  is  potable,  mineral,  or  unfit  for  drinking 
and    cooking.     Water   used    for    domestic    purposes,   such    as 
drinking,  cooking,  and  washing,  should  be  cool,  limpid,  and 
odorless,  having  a  very  feeble  but  pleasant  taste  that  should 
be  neither  bitter,  salty,  nor  sweet,  and  should  make  suds  with 
soap  without  forming  a  curd.     Water  which  possesses  these  prop- 
erties always  holds  in  solution  a  certain  quantity  of  the  gases  of 
the  air,  oxygen,  nitrogen,  and  carbon  dioxide,  and  usually  a  small 
quantity  of  mineral  matters.     The  gases  are  absolutely  essential 
to  good  water,  but  their  quantity  varies  considerably  in  different 
waters,  and  at  different  times  in   water  from   the  same  source. 
This  dissolved  air  separates  from  water  which  stands  in  a  warm 
place,  and  part  of  it  collects  on  the  sides  of  the  vessel  in  small 
bubbles,  which  we  have  all  seen  in  a  glass  of  water  that  has  stood 
for  several  hours.     Fish  cannot  live  in  water  containing  no  dis- 
solved oxygen ;  they  do  not  breathe,  but  their  gills  remove  the 
dissolved  oxygen  from  the  water  which  they  continually  draw 
through  those  organs  (see  §  33). 

The  solid  matters  in  a  potable  water  should  not  exceed  two  or 
three  decigrammes  per  litre,  and  these  matters  should  be  entirely 
mineral.  They  usually  consist  of  compounds  of  calcium  and  mag- 
nesium ;  magnesium  sulphate  and  calcium  sulphate  being  the 
most  common,  while  a  small  proportion  of  common  salt  is  gener- 
ally present. 

58.  When  larger  quantities  of  calcium  or  magnesium  com- 
pounds are  present,  the  water  is  said  to  be  hard.     The  hardness 


MINERAL    WATERS.  49 

may  be  due  either  to  sulphates  or  carbonates.  Water  dissolves 
only  a  very  small  quantity  of  calcium  sulphate,  but  then  has  a 
peculiar  taste  and  curdles  the  soap  when  we  use  it  for  washing. 
We  add  a  few  drops  of  a  solution  of  barium  chloride  to  some 
water  containing  a  little  calcium  sulphate,  and  instantly  a  white 
cloud  appears :  this  is  caused  by  the  formation  of  an  insoluble 
body  called  barium  sulphate,  and  the  test  makes  us  sure  that  the 
water  contained  a  sulphate.  Calcium  and  magnesium  carbonate 
are  insoluble  in  pure  water,  but  dissolve  in  water  containing  car- 
bonic acid  gas,  or  carbon  dioxide.  When  such  water  is  boiled,  the 
carbon  dioxide  is  driven  out,  and  then  the  carbonate  separates,  for 
it  is  no  longer  soluble.  Hence  we  have  a  method  of  curing  hard 
water  which  contains  only  calcium  carbonate  and  carbonic  acid : 
we  boil  it,  and  allow  it  to  settle,  and  after  pouring  off  the  clear 
water  expose  it  to  the  air  for  a  time,  so  that  it  may  dissolve  some 
of  the  gases  from  the  atmosphere. 

59.  Drinking-water  must  not  contain  animal  or  vegetable  sub- 
stances :   they  render  it  very  unwholesome.     Happily,  the  waters 
of  rivers,  which  become  contaminated  with  so  many  such  impuri- 
ties, generally  become  purified  during   their  exposure  to  the  air, 
because  the  foul  matter  is  gradually  oxidized.     Water  containing 
these  matters  usually  has  a  sweetish  taste  and  a  disagreeable  odor, 
which  may,  however,  be  very  faint.     It  may  be  purified  by  passing 
it  through  a  charcoal  filter  (§  227). 

60.  MINERAL  WATERS  contain  various  dissolved  mineral  mat- 
ters.    Some  are  hot,  others  warm,  and  still  others  cold.     Those 
which  effervesce  or  sparkle   contain  a  considerable  proportion  of 
carbonic  acid  gas  in  solution,  and  it  is  the  escape  of  this  gas  which 
produces  the  sparkling.     Apollinaris  water  contains,  besides  the 
carbonic  acid  gas,  principally  a  little  sodium  acid  carbonate,  com- 
mon salt,  and  magnesium  and  sodium  sulphates.     Buffalo  lithia 
water  contains  very  little  of  the  sodium  compounds,  but  consider- 
able quantities  of  calcium  sulphate,  with  carbonates  of  potassium, 
calcium,  barium,  and  lithium. 

Saratoga  water  has  a  large  proportion  of  calcium  and  magnesium 
carbonates  dissolved  by  the  excess  of  carbon  dioxide  which  it  con- 

4 


50  LESSONS    IN    CHEMISTRY. 

tains,  and  a  very  large  proportion  of  common  salt.  Gettysburg 
water  contains  principally  the  carbonates  of  calcium,  magnesium, 
and  sodium,  together  with  a  little  dissolved  silica :  its  excess  of 
carbon  dioxide  is  quite  small.  Hunyadi  Janos  contains  sulphates 
of  magnesium,  sodium,  calcium,  and  potassium ;  these  substances 
give  to  it  purgative  properties,  in  which  it  is  resembled  by  Fried- 
richshall  water,  for  the  composition  of  the  latter  is  somewhat 
similar. 

Chalybeate  waters  are  such  as  contain  either  iron  carbonate, 
held  in  solution  by  an  excess  of  carbon  dioxide,  or  ferrous  sul- 
phate :  in  the  former  case  the  water  becomes  muddy  on  exposure 
to  the  air,  for  as  the  carbon  dioxide  escapes,  ferrous  carbonate  is 
deposited.  The  Mercer  County  water,  of  Virginia,  contains  a 
large  proportion  of  ferrous  sulphate.  Iron  waters  are  usually 
cold. 

Sulphur  waters  owe  their  odors  and  their  virtues  to  hydrogen 
sulphide  and  sulphides  of  potassium  and  sodium.  They  are  gen- 
erally warm,  or  even  hot. 


LESSON    VII. 

NOMENCLATURE   OF   COMPOUNDS    OP   OXYGEN- 
OZONE.— HYDROGEN  DIOXIDE. 

* 

61.  Besides  being  able  to  express  the  composition  of  molecules 
by  chemical  formulae,  as  we  have  learned,  it  is  important  that  we 
may  have  a  distinctive  name  for  eacli  substance,  and  that  this 
name  may  express  as  far  as  possible  the  composition  of  the  mole- 
cule. A  compound  of  only  two  elements  is  called  a  binary  com- 
pound ;  one  containing  three  is  a  ternary  compound ;  one  con- 
taining four,  a  quaternary.  We  may  be  satisfied  at  present  to 
study  a  system  of  naming — a  nomenclature — for  the  binary  com- 
pounds of  oxygen.  These  are  called  oxides. 


NOMENCLATURE   OF   COMPOUNDS   OP   OXYGEN,  ETC.          51 

We  place  a  small  piece  of  phosphorus  on  a  piece  of  glass  on  a 
plate,  light  it,  and  cover  it  with  a  bell-jar  (Fig.  34).  The  phos- 
phorus combines  with  the  oxy- 
gen of  the  air,  and  the  com- 
pound which  is  formed  settles 
like  flakes  of  snow  in  the  jar 
and  on  the  plate.  This  is  an 
oxide  of  phosphorus.  On  another 
plate,  in  the  same  manner,  we 
burn  a  small  piece  of  sodium : 
we  have  here  formed  sodium 
oxide.  Now  we  rinse  out  each 
jar  and  plate  with  a  little  water : 
when  the  water  comes  in  con- 
tact with  the  oxides  that  have 
been  formed,  there  is  a  hissing  FIG.  34. 

noise,    and    the    jars    become 

warm,  showing  that  energy  has  been  developed  ;  there  is  a  chem- 
ical action  between  the  water  and  the  oxide.  We  pour  into  sepa- 
rate vessels  the  liquids  from  the  two  jars,  and  to  that  from  the 
phosphorus  oxide  we  add  some  blue  litmus  solution,  prepared  by 
boiling  litmus,  a  substance  made  from  a  peculiar  moss,  with  water. 
The  blue  color  instantly  changes  to  red.  We  pour  some  of  this 
red  liquid  into  the  water  from  the  sodium  experiment,  and  the 
blue  color  at  once  reappears.  It  is  certain  then  that  our  two 
oxides  have  different  properties,  and  the  study  of  these  and  other 
oxides  has  shown  that  when  oxygen  combines  with  a  non-metal- 
lic element,  the  resulting  oxide  usually  combines  with  water,  and 
forms  a  substance  which  changes  blue  litmus  to  red.  Such  sub- 
stances generally  have  a  sour  taste,  and  are  called  acids.  On  the 
contrary,  the  oxides  of  the  metallic  elements,  if  they  have  any 
effect,  change  the  reddened  litmus  to  blue,  and  are  called  basic 
oxides.  Many  oxides,  however,  have  no  effect  on  either  red  or 
blue  litmus. 

62.  When  an  oxide  reacts  with  water,  a  body  called  a  hydroxide 
or  hydrate  is  formed.  The  acids  containing  oxygen  are  hydrates 
corresponding  to  non-metallic  oxides,  while  the  metallic  oxides 


52  LESSONS    IN   CHEMISTRY. 

usually  have  corresponding  metallic  hydroxides,  sometimes  called 
metallic  hydrates.  We  have  seen  the  formation  of  sodium  hydrox- 
ide by  the  action  of  sodium  on  water  ;  this  same  compound  results 
from  the  action  of  water  on  sodium  oxide,  and  we  will  notice  that 
the  only  difference  between  the  hydroxide  and  water  is  that  the 
former  contains  an  atom  of  sodium  in  place  of  one  atom  of 
hydrogen. 

Na20         +     H20     =         NaOH          +         NaOH 
Sodium  oxide.        Water.     Sodium  hydroxide.    Sodium  hydroxide. 

63.  An  analysis  of  the  oxide  of  phosphorus  which  we  have 
formed,  shows  that  its  molecule  contains  phosphorus  combined 
with  five  atoms  of  oxygen  ;    it  is  therefore  called  phosphorus 
pentoxide*  and,  because  the  acid  which  it  forms  is  called  phos- 
phoric acid,   the    oxide   is  sometimes    called    phosphoric    oxide. 
In  general,  the  name  of  an  oxygen  compound  is  formed  by  putting 
oxide  after  the  name  of  the  other  element,  and  to  the  word  oxide 
is  prefixed  the  Greek  name  of  the  number  of  atoms  of  oxygen  in  a 
molecule  of  the  oxide. 

A  monoxide  contains  one  atom  of  oxygen,  a  dioxide  contains 
two  atoms  of  oxygen,  a  trioxide  contains  three,  a  tetroxide  con- 
tains four,  a  pentoxide  five. 

The  word  sesquioxide  is  sometimes  used  to  indicate  a  com- 
pound whose  molecule  contains  three  atoms  of  oxygen  and  two 
atoms  of  the  other  element :  sesqui  means  one  and  a  half.  Man- 
ganese sesquioxide  contains  Mn203. 

Sometimes  an  element  forms  more  than  one  compound  with 
oxygen.  Nitrogen  forms  five  ;  and  when  we  have  learned  that  a 
molecule  of  each  of  these  oxides  contains  two  atoms  of  nitrogen, 
the  names  will  at  once  indicate  the  composition  of  the  molecules. 

Nitrogen  monoxide,  N20. 
Nitrogen  dioxide,      N202  (really  NO). 
Nitrogen  trioxide,     N203. 
Nitrogen  tetroxide,  N20*. 
Nitrogen  pentoxide,  N205. 

64.  Frequently  when  there  are  only  two  oxides  of  an  element, 
or  when  there  are  two  of  special  importance,  the  word  oxide  is 

*  Penta— five. 

V... 


NOMENCLATURE   OF   COMPOUNDS   OF   OXYGEN,  ETC.          53 

not  changed,  but  the  name  of  the  other  element  is  made  to  end  in 
ic  or  ous.  There  are  only  two  oxides  of  mercury  ;  that  containing 
the  largest  proportion  of  oxygen  is  called  mercuric  oxide,  while 
that  containing  the  least  proportion  is  mercurous  oxide.  Their 
molecules  contain 

Mercuric  oxide,     HgO. 
Mercurous  oxide,  Hg20. 

Each  of  the  two  more  important  oxides  of  sulphur  contains  one 
atom  of  sulphur  combined  respectively  with  three  and  two  atoms 

of  oxygen. 

Sulphuric  oxide,     SO3. 
Sulphurous  oxide,  SO2. 

The  oxide  whose  name  ends  in  ic  then  contains  a  larger  propor- 
tion of  oxygen  than  that  whose  name  ends  in  ous,  and  we  should 
not  use  these  terminations  unless  there  be  two  oxides  of  the 
element. 

We  can  now  understand  what  is  meant  when  we  say  that  water 
is  hydrogen  oxide,  and  we  will  presently  learn  the  signification  of 
all  the  names  which  we  have  been  obliged  to  use. 

OZONE. 

65.  Before,  and  sometimes  during,  a  thunder-storm,  there  is 
often  a  peculiar  odor  in  the  air,  and  the  same  odor  may  be  noticed 
near  a  good  electric  machine  in  operation.    It  has  been  found  that 
the  air  has  at  the  same  time  acquired  more  active  oxidizing  prop- 
erties than  it  had  before.    It  will  even  bleach  many  coloring  mat- 
ters.    Part  of  the  oxygen  of  the  atmosphere  has  been 
changed  to  a  body  which  we  call  ozone. 

66.  We  can  produce  this  change  by  a  simple  experi- 
ment.    Under  the  surface  of  some  water  we  scrape  the 
outside  of  a  stick  of  phosphorus,  so  that  it  may  be  per- 
fectly free  from  oxide,  and  then  put  it  into  a  bottle 
containing  enough  water  to  about  half  cover  the  phos- 
phorus,  so  that  it  may  not  take  fire  (Fig.  35).    .After 

it  has  stood  for  a  little  while,  we  dip  into  the  air  in  the  bottle  a 
piece  of  paper  that  has  been  soaked  in  some  starch  boiled  in  water 
to  which  a  little  potassium  iodide  has  been  added.  We  see  that 


54 


LESSONS    IN    CHEMISTRY. 


the  paper  at  once  becomes  blue.  Now  let  us  put  a  drop  of  a  solu- 
tion of  iodine  in  alcohol  on  paper  soaked  in  starch  to  which  no 
potassium  iodide  was  added.  The  same  blue  color  appears.  Po- 
tassium iodide  is  a  compound  of  potassium  and  iodine :  part  of  the 
oxygen  of  the  air  in  the  jar  was  converted  into  ozone;  this  took 
the  potassium  away  from  the  iodine,  and  as  soon  as  the  latter  be- 
came free  it  combined  with  the  starch,  producing  the  blue  color. 
If  we  smell  the  air  in  the  bottle,  we  find  that  it  has  a  peculiar, 
and  not  very  pleasant,  odor,  by  which  ozone  may  be  identified  as 
certainly  as  by  the  chemical  test  with  potassium  iodide  and  starch. 
It  has  been  found  that  these  same  phenomena  are  produced 
by  pure  oxygen  gas  through  which  electrical  sparks  have  been 
passed  (Fig.  36),  and  that  by  the  passage  of  such  sparks  the  vol- 
ume of  the  oxygen  is  diminished, 
while  its  weight  of  course  does  not 
change.  The  increase  in  density  so 
observed  has  shown  that  ozone  is 
half  again  as  heavy  as  oxygen  :  when 
ozone  is  heated,  it  is  converted  into 
ordinary  oxygen,  and  the  volume  is 
expanded  in  the  same  proportion. 
Chemists  have  consequently  been  led 
to  believe  that  while  ordinary  oxygen 
contains  two  atoms  in  its  molecule,  a 
molecule  of  ozone  contains  three  such 
atoms.  We  may  consider,  therefore, 
that  if  a  molecule  of  ordinary  oxygen 
is  represented  by  the  formula  O2,  O3 
represents  a  molecule  of  ozone. 

67.  Let  us  see  why  ozone  possesses 
more   active    powers    than    oxygen. 

When  we  pass  electric  sparks  through  oxygen,  we  decompose  its 
molecules,  and  the  energy  of  electricity  is  transferred  to  the  atoms, 
which  it  enables  to  combine  by  threes,  instead  of  by  twos.  Phos- 
phorus is  gradually  oxidized  by  oxygen,  but  one  atom  of  phos- 
phorus does  not  combine  with  whole  molecules  of  oxygen :  we 


FIG. 


HYDROGEN    DIOXIDE.  55 

shall  in  time  learn  that  in  this  case  two  atoms  of  phosphorus  take 
three  atoms  of  oxygen  ;  that  would  be  a  molecule  and  a  half;  but, 
while  the  energy  developed  by  the  rapid  combustion  of  phosphorus 
appears  as  heat  and  light,  the  energy  developed  by  the  slow  com- 
bustion of  the  phosphorus  is  transferred  to  the  odd  atom  of  oxy- 
gen, and  .enables  it  to  combine  with  two  other  atoms  set  free  from 
molecules  in  the  same  manner. 

6P          +          602  3PZ03  +  O3 

Phosphorus,  Oxygen,  Phosphorus  trioxide,  Ozone, 

six  atoms.        six  molecules.  three  molecules.          one  molecule. 

As  ozone  contains  more  energy  than  oxygen,  its  properties  are 
more  energetic ;  thus,  a  bright  silver  coin  suspended  in  ozone 
soon  becomes  tarnished  by  oxidation. 

We  shall  have  occasion  to  study  many  actions  of  this  kind,  where 
the  energy  evolved  by  the  combination  of  certain  atoms  is  trans- 
ferred to  other  atoms,  giving  them  more  active  properties  than 
they  had  before. 

When  ozone  oxidizes  other  bodies,  in  most  cases  only  one  of  its 
atoms  is  used  in  the  oxidation ;  the  other  two  unite  to  form  a 
molecule  of  oxygen. 

When  the  moist  potassium  iodide  was  decomposed  by  ozone, 
potassium  hydroxide  was  formed;  its  molecule  contains  KOH, 
and  we  see  that  the  water  present  must  have  taken  part  in  the 
reaction,  which  we  may  write 

2KI  +  H2Q  +  O3  =  2KOH  +  0'  +  I2 

Potassium  iodide.  Potassium  hydroxide. 

68.  Ozone  is  frequently  produced  in  slow  combustions.     By 
great   cold  it  may  be   converted   into  a   sky-blue  liquid.     It 
is  destroyed,  that  is,  converted  into  oxygen,  by  a  temperature 
of  290°.    Its  oxidizing  powers  are  sometimes  employed  for  bleach- 
ing and  disinfecting,  the  ozone  in  these  cases  being  produced  by 

electricity. 

HYDKOGEN  DIOXIDE,  H2O2. 

69.  We  introduce  some  pulverized  barium  dioxide,  a  compound 
whose  molecule  contains  one  atom  of  the  metal  barium  and  two 
atoms  of  oxygen,  into  a  small  flask  containing  some  cold  dilute  hy- 
drochloric acid  ;  as  the  solid  dissolves,  a  solution  of  barium  chloride 


56  LESSONS    IN    CHEMISTRY. 

is  formed,  while  the  hydrogen  of  the  hydrochloric  acid  and  the 
oxygen  of  the  barium  dioxide  combine  to  form  a  compound  called 
hydrogen  dioxide,  which  remains  dissolved  in  the  liquid. 

BaO2  +  2HC1  =         Bad2  +  H202 

Barium  dioxide.        Hydrochloric  acid.        Barium  chloride.        Hydrogen  dioxide. 

The  separation  of  the  hydrogen  dioxide  from  the  barium  chlo- 
ride is  not  an  easy  matter,  but  the  latter  compound  will  not  inter- 
fere with  our  experiments. 

We  pour  some  of  the  liquid  on  a  little  manganese  dioxide ;  at 
once  a  brisk  effervescence  takes  place,  and  by  the  aid  of  a  match- 
stick  bearing  a  spark,  we  are  shown  that  the  tube  is  filled  with 
oxygen.  The  hydrogen  dioxide  has  been  decomposed  into  water 
and  oxygen  ;  but  the  manganese  dioxide  remains  unchanged  ;  it  is 
probably  in  fact  converted  into  a  higher  oxide,  but  the  addi- 
tional oxygen  is  at  once  taken  away  from  this  oxide  by  another 
atom  of  oxygen  with  which  it  forms  a  molecule  of  the  gas. 

In  another  tube,  we  pour  a  little  of  our  solution  on  some  black 
lead  sulphide :  the  color  quickly  changes  to  white,  and  no  gas  is 
given  off,  for  the  lead  sulphide  is  converted  into  lead  sulphate, 
while  water  is  formed. 

PbS  +  4H202  =        PbSO4        +  4H20 

Lead  sulphide.  Lead  sulphate. 

We  now  pour  a  little  hydrogen  dioxide  into  some  purple  solution 
of  potassium  permanganate  which  has  been  acidified  with  sulphu- 
ric acid.  The  liquid  becomes  colorless ;  at  the  same  time  bubbles 
of  oxygen  are  disengaged,  and  may  be  identified  by  the  usual  test. 
In  this  case  an  atom  of  oxygen,  very  loosely  held  by  the  other 
atoms  in  the  hydrogen  dioxide,  has  combined  with  another  atom 
from  the  potassium  permanganate,  which  is  very  rich  in  oxygen, 
and  a  molecule  of  free  oxygen  is  given  off,  while  water  is  formed 
as  before. 

We  mix  some  of  the  hydrogen  dioxide  liquid  with  a  little 
yellow  solution  of  potassium  dichromate  ;  we  then  quickly  pour 
in  a  quantity  of  ether,  and  briskly  shake  the  tube  ;  the  ether 
being  lighter  than  the  water,  comes  to  the  top  of  the  latter,  in 
which  it  is  almost  insoluble,  and  this  layer  of  ether  has  a  dark 


CHLORINE.  57 

blue  color.  It  contains  perchromic  acid,  a  body  which  is  formed 
by  the  oxidation  of  the  potassium  dichromate  ;  but  with  hydrogen 
dioxide  this  perchromic  acid  behaves  just  like  potassium  perman- 
ganate ;  unless  it  is  at  once  removed  from  the  liquid  in  which  it  is 
formed,  its  oxygen  is  taken  away,  and  a  green  liquid  containing  a 
lower  oxide  of  chromium  is  obtained. 

70.  "We  may  then  conclude  that  hydrogen  dioxide  acts  in  three 
ways  with  other  substances  :  sometimes  it  is  reduced,  that  is,  part 
of  its  oxygen  is  taken  away,  while  the  other  body  remains  un- 
changed, as  is  the  case  with  manganese  dioxide ;  sometimes  the 
second  substance  is  oxidized,  as  with  the  lead  sulphide  and  potas- 
sium dichromate ;  sometimes  both  the  hydrogen  dioxide  and  the 
other  body  are  deoxidized,  as  in  the  cases  of  potassium  perman- 
ganate and  perchromic  acid. 

Pure  hydrogen  dioxide  is  a  syrupy,  colorless  liquid,  without 
odor,  and  having  a  density  of  1.45.  It  is  slowly  decomposed  into 
water  and  oxygen  at  ordinary  temperatures,  with  brisk  efferves- 
cence at  100°,  and  explosively  if  dropped  on  a  surface  heated  to 
higher  temperatures ;  in  vacuo  it  may  be  distilled  without  de- 
composition. Owing  to  the  readiness  with  which  it  gives  up  oxy- 
gen, hydrogen  dioxide  will  destroy  organic  coloring  matters  and 
germs  of  disease.  It  is  extensively  manufactured  for  bleaching 
silk,  ostrich  feathers,  and  human  hair  ;  an  aqueous  solution  con- 
taining three  p^r  cent,  is  used  in  medicine  as  an  antiseptic. 

Hydrogen  dioxide  and  ozone  undergo  mutual  decomposition, 
\fater  and  free  oxygen  being  formed. 

H202  +     O3       =    H2Q    +  202 

Hydrogen  dioxide.        Ozone.        Water.        Two  molecules  of  oxygen. 


LESSON    VIII. 

CHLORINE.— CHLORIDES. 

Atomic  weight,  35.5.  Symbol,  Cl. 

71.  The  element  chlorine  has  such  strong  affinities  for  other 
elements  that  it  does  not  exist  free  in  nature,  but  is  always  found 


58 


LESSONS    IN    CHEMISTRY. 


in  combination.  The  most  important  of  its  compounds  is  common 
salt,  which  contains  sodium  and  chlorine,  and  of  which  enormous 
quantities  exist  in  the  ocean,  and  in  salt  springs  and  salt  mines. 
We  do  not  usually  prepare  chlorine  directly  from  salt,  but  from 
hydrochloric  acid,  the  latter  being  prepared  from  the  salt  itself. 

We  mix  in  a  glass  flask  some  strong  hydrochloric  acid  with 
about  one-sixth  its  weight  of  manganese  dioxide,  and,  after  adapt- 
ing to  the  flask  a  cork  through  which  passes  a  tube  for  the  exit 
of  the  gas,  and  another  tube  called  a  safety-tube,  we  gently  heat 
the  mixture  over  a  flame  (Fig.  37).  The  safety-tube  (A),  which 


O 


FIG.  37. 

is  bent  around  on  itself  and  has  a  little  bulb  blown  on  the  bend, 
enables  us  to  add  more  acid  if  necessary,  and  at  the  same  time  if 
there  should  be  too  much  pressure  in  the  flask  it  allows  the  gas 
to  escape  through  the  little  acid  which  we  must  pour  into  it: 
on  the  contrary,  when  the  flask  cools  and  the  gas  contracts  in  vol- 
ume, air  may  enter  through  the  safety-tube,  and  any  liquid  into 
which  we  may  wish  the  end  of  the  delivery-tube  to  dip,  will  not 
be  drawn  back  into  the  flask.  We  may  dry  our  chlorine  gas  by 
passing  it  through  a  bottle  containing  either  calcium  chloride  or 
strong  sulphuric  acid,  or  we  may  pass  it  directly  into  a  bottle. 


CHLORINE.  59 

Chlorine  dissolves  in  water,  and  we  collect  it  by  downward  dry 
displacement ;  for  it  is  a  heavy  gas,  and  when  we  pass  the  tube 
through  which  it  flows  to  the  bottom  of  a  jar,  the  chlorine  grad- 
ually forces  the  air  out  at  the  top.  We  might  collect  it  over  salt 
water  in  the  pneumatic  trough,  as  it  does  not  dissolve  in  salt 
water.  We  can  easily  see  when  the  jar  is  full,  for  the  gas  has  a 
greenish-yellow  color.  While  we  are  filling  several  jars,  which 
we  cover  with  glass  plates  as  soon  as  they  are  filled,  we  may  ex- 
amine the  chemical  change  by  which  chlorine  is  formed.  Man 
ganese  dioxide  contains  two  atoms  of  oxygen,  and  this  oxygen 
combines  with  the  hydrogen  of  the  hydrochloric  acid,  forming 
water.  Two  atoms  of  oxygen  require  four  atoms  of  hydrogen, 
and  for  these  four  atoms  we  will  need  four  molecules  of  hydro- 
chloric acid,  each  of  which  contains  one  atom  of  chlorine  and  one 
of  hydrogen.  The  atom  of  manganese  combines  with  two  atoms 
of  chlorine,  forming  a  body  called  manganese  chloride,  and  as 
there  were  four  chlorine  atoms  in  the  hydrochloric  acid,  two  of 
these  will  pass  off  as  gas.  We  may  write  the  reaction, 

MnO2  +  4HC1  MnC12  +  2R2Q  +  C12 

Manganese  dioxide.        Hydrochloric  acid.        Manganese  chloride.  Chlorine. 

72.  Properties. — Chlorine  is  a  greenish-yellow  gas,  having  an 
unpleasant,  suffocating  odor.  We  must  be  careful  not  to  breathe 
it  in  a  too  undiluted  form,  for  it  causes  violent  coughing,  and  irri- 
tates the  lungs.  It  is  2.45  times  as  heavy  as  an  equal  bulk  of 
air,  or  35.5  times  as  heavy  as  an  equal  volume  of  hydrogen.  Its 
atomic  weight  is  also  35.5  :  there  are  many  other  elements  whose 
atomic  weights  and  densities  (when  in  the  form  of  gas)  compared 
to  hydrogen  are  the  same,  and  we  must  suppose  that  the  mole- 
cules of  such  elements  are  like  those  of  hydrogen  in  that  each 
contains  two  atoms  (§  46).  Chlorine  dissolves  in  water :  at  ordi- 
nary temperatures,  one  litre  of  water  will  dissolve  about  two 
and  a  half  litres  of  the  gas.  It  may  be  liquefied  at  15°  by  a 
pressure  of  four  atmospheres,  that  is,  four  times  as  great  as  the 
ordinary  pressure  of  the  air. 

Chlorine  possesses  very  great  affinity  for  the  other  elements, 
and  the  compounds  which  it  forms  with  them  are  called  chlorides. 


60 


LESSONS    IN    CHEMISTRY. 


Over  one  of  our  jars  of  the  gas  we  place  a  piece  of  coarse  wire 
gauze,  through  which  we  sprinkle  some  finely-powdered  antimony. 
Each  little  particle  burns,  and  we  have  a  shower  of  fire,  while  a 
heavy  cloud  of  white  smoke  settles  in  the  jar:  this  smoke  is 
antimony  chloride.  Into  another  jar  we  throw  some  pieces  of 
Dutch  leaf,  a  very  thin  brass  used  for  cheap  gilding :  this  also 
ourns,  and  the  copper  and  zinc  of  which  the  Dutch  metal  was 
composed  are  converted  into  copper  chloride  and  zinc  chloride. 
We  may  burn  some  thin  copper  in  the  same  manner.  We  put  a 
small  piece  of  phosphorus  in  a  deflagrating-spoon,  and  lower  this 
into  another  jar :  it  burns  with  a  pale  flame  into  phosphorus 
chloride. 

73.  Of  all  the  elements,  hydrogen  is  that  for  which  chlorine 
possesses  the  most  remarkable  affinities.  In  a  room  lighted  only 
by  a  candle,  we  have  mixed  over  salt  water  equal  volumes  of 
chlorine  and  hydrogen,  and,  after  drying  this  mixture  by  passing 
it  through  a  tube  containing  pumice-stone  and  sulphuric  acid,  we 
have  filled  with  it  some  little  bulbs,  blown  on  thin  glass  tubes, 
and  then  sealed  the  ends  of  the  tubes  with  little  plugs  of  paraffin. 
It  is  easy  to  fill  the  bulb ;  we  connect  one  end  of  it  by  a  rubber 

tube  on  which  is  a  pinch 
(A),  to  the  tube  of  the 
bell-jar  in  which  the  mix- 
ture is  made ;  then  on 
pressing  the  jar  into  the 
salt  water  and  loosing  the 
pinch,  the  gas  is  forced 
through  the  bulb  (Fig. 
FIG.  38.  38).  We  keep  these  bulbs 

carefully  covered  from  the 

light.  We  now  uncover  one,  put  it  behind  a  sheet  of  glass,  and 
then,  standing  at  a  little  distance,  burn  a  piece  of  magnesium  wire. 
Instantly  there  is  an  explosion  ;  the  hydrogen  and  chlorine  have 
combined.  The  combination  is  brought  about  in  the  same  manner 
by  direct  sunlight,  and  more  gradually  by  diffuse  daylight. 

Chlorine  does  not  support  ordinary  combustion,  for  it  does  not 


CHLORINE. — CHLORIDES.  61 

combine  directly  with  carbon,  and  ordinary  combustibles  contain 
hydrogen  and  carbon  ;  but  their  hydrogen  may  burn  in  chlorine. 
We  put  a  lighted  taper  into  a  jar  of  chlorine,  and  the  flame  be- 
comes red  and  smoky :  the  chlorine  combines  with  the  hydrogen 
of  the  wax,  but  the  carbon  separates  in  the  form  of  smoke. 

Chlorine  even  decomposes  many  compounds  containing  hydro- 
gen, taking  away  that  element  to  form  hydrochloric  acid.  The 
solution  of  chlorine  in  water  is  decomposed  by  sunlight,  the  oxy- 
gen being  set  free. 

2C12  +  2H20  =  4HC1  +  O2 

Into  a  jar  with  straight  sides,  filled  with  chlorine,  we  rapidly 
introduce  a  paper  saturated  with  turpentine,  and  quickly  replace 
the  cover  of  the  jar.  There  is  a  flash  of  red  light,  and  a  cloud  of 
smoke.  Turpentine  is  a  compound  of  carbon  and  hydrogen  only  : 
the  chlorine  combines  with  the  hydrogen,  and  the  carbon  forms 
the  smoke.  We  find  after  the  experiment  that  the  paper  is  not 
burned :  we  use  a  plain  straight  jar,  because  it  is  easily  cleaned  by 
rubbing  with  a  little  turpentine. 

We  pour  some  blue  litmus-water  into  a  jar  of  chlorine ;  the 
blue  liquid  becomes  colorless.  In  another  jar  we  suspend  a  piece 
of  moist  colored  calico,  and  it  quickly  fades.  Chlorine  possesses 
bleaching  properties,  and  these  properties  are  due  to  the  decompo- 
sition of  the  dye-stuffs,  nearly  all  of  which  contain  hydrogen  that 
the  chlorine  may  remove.  For  the  same  reason  chlorine  is  a  val- 
uable disinfectant,  for  most  unpleasant  and  unwholesome  odorous 
matters  are  compounds  of  hydrogen. 

74.  Chlorides. — The  binary  compounds  of  chlorine  are  called 
chlorides,  and  the  same  prefixes  which  are  used  for  the  names  of 
the  oxides  are  employed  also  to  indicate  the  number  of  chlorine 
atoms  in  a  molecule  of  the  compound  ;  thus,  phosphorus  trichloride 
contains  PCI3.  In  general,  these  prefixes  are  used  to  indicate  the 
number  of  atoms  of  the  second  named  element  with  which  one  or 
more  atoms  of  that  first  named  are  combined.  When  there  are 
only  two  chlorides  which  are  important,  the  terminations  ous  and 
ic  designate  which  contains  the  least  and  the  greatest  proportion 
of  chlorine  (see  §  64).  .Mercurous  chloride  is  Hg'2CP  ;  mercuric 


62  LESSONS    IN    CHEMISTRY. 

chloride  is  HgCP ;  this  nomenclature  also  is  of  general  applica- 
tion. 

The  metallic  chlorides  are  all  soluble  in  water,  with  the  excep- 
tion of  silver  chloride,  AgCl,  mercurous  chloride,  Hg2Cl2,  and 
cuprous  chloride,  Cu'2CP.  Lead  chloride  is  only  slightly  soluble. 
The  non-metallic  chlorides,  as  a  rule,  are  decomposed  by  water, 
and  in  such  cases  part  or  all  the  chlorine  combines  with  hydro- 
gen, forming  hydrochloric  acid.  Thus,  phosphorous  chloride, 
POP,  yields  phosphorous  acid  and  hydrochloric  acid. 

PCI3  +  3H20  =  H3P03  +  3HC1 

Phosphorous  chloride.  Phosphorous  acid.        Hydrochloric  acid. 

75.  We  pour  a  few  drops  of  a  solution  of  silver  nitrate  in  pure 
water  into  some  water  in  which  common  salt,  which  is  sodium 
chloride,  has  been  dissolved.  At  once  a  white  precipitate  forms, 
for,  while  sodium  nitrate  now  exists  in  solution,  silver  chloride  is 
formed,  and  this  is  insoluble. 

AgNO3      +          NaCl  =        NaNO3        +        AgCl 

Silver  nitrate.        Sodium  chloride.        Sodium  nitrate.        Silver  chloride. 

The  precipitate  darkens  on  exposure  to  light,  and  this  reaction 
enables  us  to  determine  whether  a  body  contains  or  does  not  con- 
tain a  chloride.  All  solutions  of  chlorides  give  the  white  precipi- 
tate, which,  we  may  add,  dissolves  if  we  pour  off  most  of  the 
liquid  and  then  shake  the  white  powder  with  strong  ammonia- 
water. 


LESSON    IX. 
HYDROCHLORIC  ACID.— ACIDS.— SALTS. 

76.  Hydrochloric  Acid,  HC1. — We  have  seen  that  this  com- 
pound is  formed  by  the  direct  union  of  chlorine  and  hydrogen, 
and  by  the  action  of  water  on  certain  chlorides.  Many  chlorides 
are  decomposed  by  water  at  high  temperatures,  and  in  this  manner 
some  mineral  chlorides  existing  in  the  rocks  cause  hydrochloric 


HYDROCHLORIC   ACID. 


63 


acid  to  be  formed  in  certain  volcanic  regions,  where  it  mixes  with 
the  other  gases  that  are  emitted. 

7*7.  Preparation. — Hydrochloric  acid  is  made  by  the  action  of 
sulphuric  acid  on  common  salt,  the  sodium  of  the  salt  changing 
places  with  the  hydrogen  of  the  sulphuric  acid. 

We  put  some  pieces  of  rock-salt  in  a  flask  like  that  in  which 
we  made  chlorine,  and,  if  we  wish  a  solution  of  the  gas,  we  con- 
nect our  delivery-tubes  with  a  series  of  bottles  containing  water, 
through  which  the  gas  will  be  forced  to  bubble  (Fig.  39).  If  we 

0 


FIG. 


wish  the  dry  gas,  we  dry  it  as  we  did  the  chlorine.  When  all  is 
ready,  we  pour  through  the  safety-tube  sulphuric  acid  which  we 
have  previously  diluted  with  an  equal  volume  of  water,  and  im- 
mediately the  gas  begins  to  come  off.  When  the  reaction  becomes 
tranquil,  we  must  heat  the  mixture. 

One  molecule  of  sulphuric  acid  contains  two  atoms  of  hydrogen, 
and  may  be  made  to  yield  one  or  two  molecules  of  hydrochloric 
acid,  by  reacting  with  one  or  with  two  molecules  of  salt. 

NaCl          +       H2SO*        =  HC1  +          NaHSO* 

Sodium  chloride.      Sulphuric  acid.      Hydrochloric  acid.      Sodium  acid  sulphate. 

2NaCl  +  H2SO*  =  2HC1  +         Na2S04 

Sodium  sulphate. 


64  LESSONS    IN    CHEMISTRY. 

This  reaction  is  operated  on  an  enormous  scale  in  Europe, 
where  the  sodium  sulphate  is  afterwards  converted  into  soda  or 
sodium  carbonate. 

78.  Properties, — Hydrochloric  acid  is  a  colorless,  pungent,  and 
suffocating  gas.     Its  density  compared  to  hydrogen  is  18.33,  suf- 
ficiently near  that  which  would  be  indicated  by  half  its  molecular 
weight,  which   is  36.5  (see  §  48).     It  is  very  soluble  in  water, 
and  if  under  the  surface  of  water  we  remove  the  cork  from  a  bot- 
tle filled  with  the  gas,  the  water  at  once  rises  and  fills  the  bottle. 
At  0°  one  litre  of  water  will  dissolve  500  litres  of  hydrochloric 
acid.     The  strongest  hydrochloric  acid  of  commerce,  commonly 
called  muriatic  acid,  contains  about  34  per  cent,  of  the  gas.     Like 
the  gas,  it  produces  fumes  in  the  air,  some  gas  escaping  from  it 
and  condensing  the  moisture  in  the  atmosphere. 

Hydrochloric  acid  is  a  strong  acid.  A  drop  or  two  of  the  solu- 
tion will  redden  a  large  quantity  of  blue  litmus.  We  slowly  pour 
some  hydrochloric  acid  into  a  strong  solution  of  sodium  hydrox- 
ide :  a  white  powder  soon  separates,  and  we  can  satisfy  ourselves 
by  tasting  it  that  this  is  common  salt.  Water  also  is  formed. 

NaOH         +  HC1  =  H2Q  +         NaCl 
Sodium  hydroxide.  Sodium  chloride. 

With  oxides  of  the  metals,  hydrochloric  acid  acts  in  the  same 
manner,  water  and  a  chloride  being  formed. 

HgO          +  2HC1  =          HgCl2  +  H2Q 

Mercuric  oxide.  Mercuric  chloride. 

We  have  seen  that  zinc  liberates  the  hydrogen  from  hydro- 
chloric acid  :  many  other  metals  act  likewise. 

ACIDS   AND    SALTS. 

79.  An  acid  is  a  compound  containing  hydrogen  which  is  ca- 
pable of  being  replaced  by  a  metal,  forming  a  body  which  is  called 
a  salt.    Although  salts  may  be  formed  in  various  manners,  we  have 
an  exact  definition  :  a  salt  represents  an  acid  whose  hydrogen  has 
been  partly  or  wholly  replaced  by  metal.     Hydrochloric  acid  is  an 
example  of  a  binary  acid,  but  the  few  binary  acids  which  we  shall 
study  have  not  all  as  energetic  properties  as  hydrochloric  acid. 
The  salts  formed  by  hydrochloric  acid  are  of  course  the  chlorides. 


HYPOCHLOROUS   OXIDE   AND    ACID.  65 

80.  Hypochlorous  Oxide  and  Acid, — When  chlorine  is  passed 
over  cooled  mercuric  oxide,  mercuric  chloride  is  formed,  and  the 
oxygen  which  separates  from  the  mercury  combines  with  chlo- 
rine, forming  a  gas  which  may  be  condensed  to  a  yellow  liquid 
by  passing  it  into  a  bottle  surrounded  by  a  freezing  mixture  of 
ice  and  salt. 

HgO  +      2C12  =        HgCl2  +  C120 

Mercuric  oxide.  Mercuric  chloride.  Hypochlorous  oxide. 

This  is  hypochlorous  oxide ;  it  is  a  dangerous  body,  and  often 
explodes  without  warning. 

It  reacts  with  water  in  a  manner  which  we  must  study.  A 
molecule  of  the  oxide  and  a  molecule  of  water  interchange  a  chlo- 
rine atom  for  a  hydrogen  atom,  and  a  compound  called  hypochlo- 
rous acid  is  formed. 

C10C1  +  HOH   =  HOCl  +  C10H 

Hypochlorous  oxide.        Water.        Hypochlorous  acid.        Hypochlorous  acid. 

This  is  an  oxygen  acid,  and  we  may  consider  that  it  is  com- 
posed of  an  atom  of  chlorine  combined  with  the  residue  of  a  mol- 
ecule of  water  from  which  one  atom  of  hydrogen  has  been  removed. 
This  residue  would  be  OH,  and,  because  the  atom  of  oxygen  has 
not  enough  hydrogen  to  satisfy  the  affinities,  it  is  not  a  molecule ;  it 
cannot  exist  except  as  part  of  a  molecule ;  that  is,  combined  with 
some  other  atom.  It  is  called,  for  convenience'  sake,  hydroxyl,  and 
all  oxygen  acids  contain  this  group  of  two  atoms,  hydroxyl.  In- 
deed, all  the  compounds  we  call  hydroxides  contain  the  group 
hydroxyl ;  thus,  potassium  hydroxide  is  KOH. 

81.  We  have  had  occasion  to  notice  the   names  hydrochloric 
acid,  hypochlorous  acid,  sulphuric  acid.     We  have  seen  that  hy- 
drochloric acid  produces  binary  salts :  the  names  of  binary  com- 
pounds, with  the  exception  of  acids,  end  in  ide,  and  we  can  now 
even  understand  that  a  sulphide  is  a  compound  containing  sulphur 
and  one  other  element.     But  hypochlorous  acid  and  sulphuric 
acid  are  not  binary  compounds ;  they  may  be  formed  respectively 
by  the  action  of  hypochlorous  and  sulphuric  oxides  on  water.    The 
first  of  these  actions  we  have  studied  :  the  second  we  may  write 

SO3  +  H20  =  H2SO*. 
5 


56  LESSONS    IN    CHEMISTRY. 

When  the  hydrogen  of  either  of  these  oxygen  acids  is  replaced 
by  metal,  how  shall  we  name  the  resulting  salts  ?  Chemists  have 
agreed  that  the  termination  ic  shall  be  changed  to  ate,  and  ous 
shall  be  changed  to  ite.  This  is  a  simple  nomenclature.  The  salts 
of  sulphuric  acid  must  be  sulphates  ;  those  of  nitric  acid,  nitrates  ; 
those  of  permanganic  acid,  permanganates  ;  those  of  hypochlorous 
acid,  hypochlorites  ;  those  of  sulphurous  acid,  sulphites.  We  see 
also  that  the  chlorates  must  be  the  salts  of  chloric  acid ;  the  ar= 
senites,  those  of  arsenious  acid. 

82.  Hypochlorites. — Solutions  of  the  hypochlorites  of  potas- 
sium and  sodium  are  useful  as  disinfecting  and  bleaching  liquids. 
They  are  made  by  passing  chlorine  gas  into  a  rather  dilute  solu- 
tion of  potassium  hydroxide  or  sodium  hydroxide ;  at  the  same 
time  water  is  formed,  and  a  chloride,  which  remains  in  solution. 

2NaOH         +  Cl2  =  NaOCl  +  NaCl  +  H20 

Sodium  hydroxide.  Sodium  hypochlorite.    Sodium  chloride. 

Such  a  liquid  quickly  removes  the  stains  of  wine  and  fruits 
from  linen,  and  also  deodorizes  offensive  matters. 

Bleaching  powder,  or  chlorinated  lime,  is  made  by  passing  chlo- 
rine gas  over  slaked  lime.  Its  solutions  contain  calcium  hypo- 
chlorite, Ca(ClO)2,  and  may  be  substituted  for  the  liquids  which 
we  have  just  mentioned.  The  bleaching  and  disinfecting  by  these 
substances  are  due  to  their  decomposition,  which  we  may  suppose 
first  sets  free  hypochlorous  acid,  and  this  attacks  the  coloring 
matter  or  offensive  substance,  removing  hydrogen  ;  the  chlorine 
atom  will  take  one  atom  of  hydrogen,  forming  hydrochloric  acid, 
and  the  group  OH  takes  another  atom,  forming  water.  We  may 
understand  this  by  examining  the  reaction  between  hydrochloric 
and  hypochlorous  acids,  which  yields  chlorine  and  water. 
HC10  +  HC1  =  H2Q  +  Cl2 

83.  Chlorates. — We  pass  a  current  of  chlorine   gas   into  a 
strong  solution  of  potassium  hydroxide,  and  a  white  solid  matter 
soon  appears  in  the  liquid ;  when  this  no  longer  increases  in  bulk, 
we  stop  the  chlorine,  heat  the  liquid  until  it  boils,  and  if  all  of  the 
solid  dissolves,  we  evaporate  it  until  a  considerable  quantity  of 
this  matter  again  separates.     We  now  allow  it  to  settle  a  moment, 


CHLORIC    ACID. — CHLORATES.  67 

and  pour  off  the  clear  liquid  :  as  this  cools,  shining  little  crystals 
separate  in  rhomboidal  plates.  These  are  potassium  chlorate,  and 
we  have  been  obliged  to  separate  them  from  potassium  chloride, 
which,  together  with  water,  is  also  formed  during  the  experiment. 

6KOH          +  3d2        =        5KC1  +        KC1Q3  +  SH'O 

Potassium  hydroxide.  Potassium  chloride.        Potassium  chlorate. 

Potassium  chlorate  is  the  most  important  salt  of  chloric  acid, 
HC103,  which  we  might  prepare  from  the  salt  by  a  troublesome 
process.  Potassium  chlorate  is  not  very  soluble  in  cold  water, 
but  is  very  soluble  in  boiling  water.*  Its  solution  is  excellent  as  a 
gargle  for  sore  throat,  but  must  not  be  swallowed,  for  it  is  poison- 
ous. We  have  seen  that  potassium  chlorate  is  decomposed  by 
heat,  yielding  oxygen  :  it  readily  gives  up  its  oxygen,  for  the 
chlorine  has  a  much  stronger  affinity  for  the  potassium  than  for 
the  oxygen,  which  appears  to  hold  the  chlorine  and  potassium 
atoms  together. 

84.  Chloric  acid,  which  would  be  set  free  by  the  action  of 
stronger  acids  on  potassium  chlorate,  is  at  once  decomposed  under 
such  circumstances  if  oxidizable  substances  be  present.  On  a 
mixture  of  equal  parts  of  potassium  chlorate  and  sugar,  powdered 
separately,  we  let  fall  a  drop  of  strong  sulphuric  acid.  The  mix- 
ture at  once  takes  fire  and  burns  vividly,  the  potassium  chlorate 
furnishing  the  oxygen  for  the  combustion  of  the 
sugar. 

Into  a  tall  jar,  filled  with  water,  we  throw  some 
crystals  of  potassium  chlorate,  and  on  them  a  small 
piece  of  phosphorus ;  then,  by  means  of  a  funnel- 
tube  which  passes  to  the  bottom  of  the  jar,  we  pour 
some  strong  sulphuric  acid  on  the  chlorate.  The 
chloric  acid  set  free  is  decomposed  by  the  phos- 
phorus and  causes  its  combustion  under  the  water 
(Fig.  40). 

We  put  into  a  mortar  a  piece  of  sulphur  about  as 
large  as  a  match-head,  and  a  crystal  of  potassium 
chlorate  of  the  same  size  ;  then  we  rub  them  briskly  together,  being 
careful  to  keep  the  mortar  far  enough  from  the  face,  and  soon  there 


68  LESSONS    IN   CHEMISTRY. 

is  a  loud  report;  the  sulphur  has  been  oxidized  and  the  potassium 
chlorate  decomposed.  If  we  used  larger  quantities  of  these  sub- 
stances in  our  experiment,  we  might  break  the  mortar,  and  possibly 
injure  our  person. 


LESSON    X. 
BROMINE.— IODINE.— FLUORINE. 

85.  Bromine,  Br  =  80. — In  a  long  tube  closed  at  one  end, 
we  dissolve  in  a  little  water  a  few  crystals  of  a  white  substance, 
called  potassium  bromide,  and  then  pour  in  some  chlorine-water, 
which  we  have  prepared  by  passing  chlorine  through  water  con- 
tained in  bottles  such   as  were  used  in  the  preparation  of  the 
solution  of  hydrochloric  acid :  we  now  add  a  considerable  propor- 
tion of  ether,  and  shake  the  tube  after  closing  it  with  the  finger. 
The  liquid  becomes  brown,  and  after  standing  a  few  minutes,  the 
ether,  which  is  not  very  soluble  in  water,  comes  to  the  surface, 
and  its  color  is  red,  while  the  water  has  become  colorless.     The 
potassium  bromide,  a  compound  of  potassium  and  bromine,  has 
been  decomposed  by  the  chlorine,  and  potassium  chloride  formed 
in  the  solution,  while  the  bromine  set  free  has  been  dissolved  by 
the  ether,  in  which  it  is  much  more  soluble  than  in  water.     We 
may  write  the  reaction, 

2KBr         +  C12     =     2KC1  -f       Br2 

Potassium  bromide.  Potassium  chloride.        Bromine. 

86.  The  compounds  of  bromine  with  potassium,  sodium,  and 
magnesium,  which  compounds  are  called  bromides  of  those  metals, 
are  found  in  the  waters  of  many  salt  springs,  and  exist  in  small 
quantity  in  the  water  of  the  ocean.     As  they  are  much  more 
soluble  in  water  than  common  salt,  they  remain  dissolved  when 
most  of  the  salt  has  been  separated  by  evaporating  the  liquid,  and 
from  their  concentrated  solution  so  obtained  the  bromine  is  sepa- 
rated by  heating  the  liquid  with  sulphuric  acid  and  manganese 


BROMINE. — IODINE.  69 

dioxide.  Supposing  all  of  the  bromine  to  exist  as  potassium 
bromide,  manganese  sulphate,  potassium  sulphate,  and  water  are 
formed ;  the  bromine  distils,  and  is  condensed  in  suitable  apparatus. 

2KBr     +       MnO2      +    2WSO*    ==    K'SO*     +     MnSO*  +  2H2Q  +  Br* 
Potassium        Manganese        Sulphuric        Potassium        Manganese 
bromide.  dioxide.  acid.  sulphate.  sulphate. 

Chlorine  is  similarly  separated  from  chlorides  by  heating  them 
with  manganese  dioxide  and  sulphuric  acid. 

87.  Bromine  is  a  dark-red  liquid,  having  an  exceedingly  irri- 
tating odor.    Its  density  is  3.2.    It  freezes  at  — 7.3°,  and  boils  at 
59°  ;  it  is  very  volatile  at  ordinary  temperatures.     It  dissolves  in 
about  thirty  times  its  weight  of  water  at  15°,  and  is  quite  soluble 
in  ether,  chloroform,  and  carbon  disulphide,  liquids  which  dissolve 
many  substances  that  are  not  soluble  in  water. 

Bromine  closely  resembles  chlorine  in  its  chemical  reactions, 
but  its  affinities  are  not  as  powerful.  Its  solution  in  water  will 
bleach  litmus,  and  other  coloring  matters,  but  more  feebly  than 
chlorine.  We  pour  a  little  bromine  into  a  deep  test-tube  and 
drop  in  a  piece  of  warm  copper  foil  which  is  instantly  converted 
into  copper  bromide  with  the  production  of  heat  and  light. 

Bromine  combines  with  hydrogen,  forming  hydrobromic  acid, 
HBr,  a  gas  which  closely  resembles  hydrochloric  acid. 

Bromine  is  exceedingly  corrosive  to  animal  tissues,  and  is 
sometimes  employed  as  a  caustic  in  surgery.  It  disinfects  like 
chlorine,  for  which  the  dilute  aqueous  solution  of  bromine  is 
often  substituted. 

The  atomic  weight  of  bromine  is  80,  and  the  density  of  its 
vapor  compared  to  hydrogen  is  also  80,  showing  that  a  molecule 
of  bromine  contains  two  atoms. 

88.  Iodine,  I  =  127. — In  a  tube  like  that  which  we  used  in 
the  experiment  with  potassium  bromide,  we  dissolve  a  little  potas- 
sium iodide  in  water,  add  chlorine-water  as  before,  and  then,  in- 
stead of  ether,  we  pour  in  some  carbon  disulphide.    After  shaking 
the  tube,  and  allowing  it  to  stand,  the  carbon  disulphide,  being 
heavier  than  the  water,  is  found  at  the  bottom  with  a  beautiful 
purple  color.     Were  we  to  pour  off  the  watery  liquid  and  allow 


70  LESSONS   IN   CHEMISTRY. 

this  carbon  disulphide  to  evaporate  in  a  shallow  dish,  it  would  leave 
a  brownish-gray  matter,  which  is  iodine,  and  which  the  chlorine 
has  driven  out  of  the  potassium  iodide,  just  as  it  separated  the 
bromine  from  the  potassium  bromide. 

89.  Like  bromine,  iodine  is  found  combined  with  potasssium, 
sodium,  and  magnesium  in  the  waters  of  some  springs,  and  in  sea- 
water.     Compounds  of  iodine  also  exist  in  the  sodium  nitrate 
found  in  large  deposits  in  Chili,  and,  being  very  soluble  in  water, 
remain  in  the  mother-liquor,  as  it  is  called,  from  which  this 
sodium  nitrate  has  been  crystallized  for  its  purification .    Iodine  is 
obtained  from  these  liquids,  and  from  the  ashes  of  sea-weeds ;  the 
sea-weeds  are  burned,  and  the  iodides  which  are  dissolved  out  of 
the  ashes  by  water,  are  treated  just  as  the  bromides  are  treated 
for  the  preparation  of  bromine.     Iodine  may  also  be  separated  by 
adding  nitric  acid  to  the  solution  of  an  iodide,  and  we  may  make 
the  experiment  by  pouring  a  little  nitric  acid  on  some  potassium 
iodide  solution  in  a  test-tube.     Potassium  nitrate  is  formed,  and 
iodine  deposits  as  a  dark  powder :  the  red  vapors  that  are  given 
off  are  a  compound  of  nitrogen  and  oxygen,  which  we  will  study 
in  good  time. 

90.  Iodine  is  purified  by  sublimation ;  that  is,  heating  it,  and 
condensing  the  vapor.     When  pure,  it  is  in   crystalline,  bluish- 
gray  plates,  much  like  scales  of  plumbago.     Its  density  is  4.95. 
It  melts  at  114°,  and  boils  at  184°.     We  carefully  heat  a  few 
small  scales  of  iodine  in  a  large  glass  flask,  which  soon  becomes 
filled  with  a  magnificent  purple  vapor.     This  vapor  is  so  heavy 
that  we  may  pour  it  out  on  a  piece  of  cold  glass,  where  it  con- 
denses in  minute  crystals.     Below  600°  the  density  of  iodine 
vapor  is  127,  but  above  1400°  only  about  half  as  much ;  each 
I2  molecule  breaks  up  into  two  single  atoms. 

Iodine  is  very  slightly  soluble  in  water  :  one  part  of  iodine  re- 
quires 7000  parts  of  water  to  dissolve  it,  and  yet  the  solution  has 
a  distinct  brown  color.  It  dissolves  readily  in  alcohol,  ether, 
chloroform,  and  carbon  disulphide,  and  the  color  of  the  solution 
depends  on  the  solvent ;  that  in  alcohol  is  brown,  but  that  in 
chloroform  is  violet. 


FLUORINE.  71 

91.  We  have  made  some  thin  starch  paste  by  boiling  starch 
with  water,  and  we  pour  some  of  this  into  two  test-tubes  :  to  the 
first  we  add  a  few  drops  of  a  solution  of  iodine  in  water,  and  the 
liquid  becomes  dark  blue ;  to  the  other  we  add  a  drop  or  two  of  a 
solution  of  potassium  iodide,  and  no  color  is  produced.  Starch  is 
dyed  a  blue  color  by  iodine,  but  the  iodine  must  be  free ;  on  add- 
ing a  few  drops  of  chlorine-water  or  nitric  acid  to  the  second 
tube  the  potassium  is  removed  from  the  iodine,  and  the  blue 
color  at  once  appears.  This  is  the  test  for  iodine. 

Iodine  combines  with  hydrogen  to  form  hydriodic  acid,  HI,  a 
gas  whose  properties  are  much  like  those  of  hydrochloric  acid.  It 
is  made  by  heating  water  with  iodine  and  amorphous  phos- 
phorus. 

92.  Analogies  of  Cl,  Br,  and  I. — On  comparing  the  three  elements  which 
we  have  just  considered,  we  find  that  while  one  is  a  gas,  another  liquid,  and 
the  third  solid,  still  the  corresponding  compounds  formed  by  each  are  much 
alike  in  chemical  nature;  that  is,  the  composition  and  reactions  of  the  mole- 
cule. The  compounds  with  hydrogen  each  contain  one  atom  of  hydrogen  com- 
bined with  one  of  the  other  element :  if  the  power  to  combine  with  one  atom 
of  hydrogen  be  taken  as  the  measure  of  the  combining  power  of  any  atom, 
the  atoms  of  chlorine,  bromine,  and  iodine  must  have  equal  powers.  Since 
an  atom  of  each  of  these  elements  combines  with  only  one  atom  of  hydrogen, 
they  are  said  to  be  monatomic  elements  in  their  compounds  with  hydrogen. 
But  their  affinities,  or  energies  of  combination,  for  hydrogen  are  not  alike : 
chlorine  will  take  the  hydrogen  away  from  hydrobromio  acid,  and  bromine 
will  take  it  away  from  hydriodic  acid.  This  is  also  the  order  of  their  affinity 
for  the  metals,  but  in  the  number  of  atoms  of  either  chlorine,  bromine,  or 
iodine  which  will  combine  with  one  atom  of  another  element,  the  three  are 
exactly  alike. 

In  this  last  respect  the  next  element  resembles  the  three  which  we  have  just 
studied. 

93.  Fluorine,  F  =  19. — We  have  coated  one  side  of  a  glass 
plate  with  wax,  and  in  the  wax  we  trace  a  design  with  a  sharp 
point,  taking  care  that  our  lines  go  quite  through  to  the  glass. 
In  a  shallow  dish  made  of  sheet  lead,  we  mix,  by  the  aid  of  a 
wooden  stick,  some  powdered  fluor-spar,  which  is  a  mineral,  with 
strong  sulphuric  acid  ;  over  this  we  place  our  glass  containing  the 
design,  with  the  waxed  side  down,  and  we  gently  warm  the  dish 
(Fig.  41).  In  a  few  minutes  we  remove  the  glass,  and,  after 


*72  LESSONS   IN   CHEMISTRY. 

gently  warming  it,  rub  off  the  wax :  we  find  that  the  design  is 
permanently  etched  into  the  glass.  The  fluor-spar  is  a  compound 
of  the  elements  fluorine  and  calcium,  and  the  sulphuric  acid  has 


FIG.  41. 

decomposed  it,  forming  a  vapor  called  hydrofluoric  acid,  a  com- 
pound of  hydrogen  and  fluorine. 

CaF2  +         H'SO4        =  CaSO*  +  2HF 

Calcium  fluoride.        Sulphuric  acid.        Calcium  sulphate.        Hydrofluoric  acid. 

Hydrofluoric  acid  may  be  condensed  to  a  liquid,  and  it  may 
be  dissolved  in  water,  but  neither  the  liquid  nor  the  solution  can 
be  kept  in  glass  bottles,  because  fluorine  has  an  extraordinary 
affinity  for  the  silicon  which  forms  part  of  the  glass,  and  would 
combine  with  that  element,  destroying  both  bottle  and  acid.  It 
is  to  this  affinity  that  we  owe  the  etching  of  our  glass  plate. 
Bottles  of  india-rubber  or  of  lead  are  used  to  contain  hydrofluoric 
acid,  for  it  does  not  attack  those  substances.  The  graduations  on 
delicate  chemical  apparatus,  such  as  the  eudiometers  we  have  seen, 
are  etched  into  the  glass  by  this  acid.  Hydrofluoric  acid  is  very 
corrosive,  and  we  must  be  careful  in  its  use. 

The  powerful  affinities  of  fluorine  long  prevented  its  isolation.  It  has  been 
obtained  by  electrolyzing  anhydrous  hydrofluoric  acid  at  low  temperatures  in 
vessels  of  platinum.  It  is  a  yellowish  gas  possessing  a  penetrating  odor.  It 
liquefies  at  very  low  temperatures.  The  density  is  18.2. 

With  hydrogen  it  combines  with  explosive  violence  even  in  the  dark  and  at 
low  temperatures.  It  decomposes  water  with  formation  of  hydrofluoric  acid 
anfl  ozone,  and  displaces  chlorine  from  its  compounds.  Most  of  the  non- 
metallic  elements  and  nearly  all  the  metals  burn  in  fluorine :  even  gold  and 
platinum  combine  with  it  at  higher  temperatures,  but  for  oxygen  it  seems  to 
have  no  affinity. 

Besides  fluor-spar,  there  is  another  important  compound  of  fluorine  found 
in  nature ;  it  is  the  mineral  cryolite,  which  is  a  compound  of  sodium  fluoride 
with  aluminium  fluoride,  SNaFAlF3. 


SULPHUR. — HYDROGEN    SULPHIDE. 


73 


LESSON    XL 


SULPHUR.— HYDROGEN   SULPHIDE. 

94.  Sulphur,  S  =  32. — We  are  all  familiar  with  sulphur,  or 
brimstone.  In  some  localities  it  is  found  pure  or  very  impure 
and  mixed  with  the  soil :  especially  is  this  the  case  in  volcanic 
countries.  Besides  this  free  or  native  sulphur,  as  it  is  called,  sul- 


FIG.  4. 

phur  is  found  combined  with  many  metals,  and  the  compounds 
are  called  sulphides. 

Crude  sulphur  comes  in  large  quantities  from  Sicily,  where  it 
is  obtained  by  heating  the  ore  so  that  the  sulphur  melts  and 
flows  from  the  earthy  matters  with  which  it  is  mixed.  It  is 
refined  by  distilling  it  in  an  apparatus  consisting  of  an  iron 
boiler  (A,  Fig.  42),  above  which  is  a  reservoir  (C)  where  the 
sulphur  is  first  melted  by  the  waste  heat,  and  from  which 
it  runs  into  the  boiler.  The  sulphur  vapor  enters  a  large 


74  LESSONS    IN    CHEMISTRY. 

chamber  (B),  and  after  condensing  runs  down  on  the  floor,  which 
is  inclined  so  that  the  melted  sulphur  may  be  drawn  off  at  a  tap 
(H).  While  the  walls  of  this  chamber  are  yet  cold,  the  sulphur 
condenses  in  a  fine  yellow  powder,  which  is  sold  as  flowers  of  sul- 
phur; but  when  the  chamber  becomes  heated,  the  condensed  sul- 
phur melts,  and  after  being  drawn  from  the  opening  is  cast  in 
cylindrical  moulds,  in  which  it  solidifies  and  becomes  roll  sulphur. 

Large  quantities  of  sulphur  are  also  obtained  by  distilling  iron 
pyrites,  a  compound  which  contains  iron  and  sulphur,  and  which 
gives  up  part  of  its  sulphur  when  it  is  heated. 

95.  PROPERTIES. — Sulphur  is  a  brittle,  lemon-yellow  solid, 
having  neither  taste  nor  odor.  It  is  a  bad  conductor  of  electricity 
and  heat :  a  piece  of  roll  sulphur  held  firmly  in  the  hand  produces 
a  curious  crackling  noise,  because  the  outside  becomes  warm,  and 
its  expansion  causes  it  to  crack  before  the  heat  can  be  conducted 
to  the  interior.  Sulphur  is  not  soluble  in  water,  is  very  slightly 
soluble  in  alcohol  and  ether,  but  dissolves  readily  in  carbon  disul- 
phide.  When  heated,  it  melts  at  114.5°,  and  becomes  a  mobile, 
amber-colored,  and  transparent  liquid. 

We  melt  some  sulphur  in  an  earthen  crucible,  and,  as  soon  as  it 
has  all  melted,  we  allow  it  to  cool  until  a  crust  forms  over  the 
surface.  We  now  make  a  hole  in  the  crust,  and  pour  out  the  sul- 
phur which  has  not  solidified.  On  breaking  off  the  crust,  we  find 
the  interior  of  the  crucible  lined  with  beautiful,  transparent  crys- 
tals, which  on  close  examination  we  determine  to  be  monoclinic 
prisms.  In  a  glass  flask  we  melt  some  more  sulphur,  but  after 
it  has  melted  we  keep  on  heating  it :  we  see  that  the  color 
becomes  darker,  and  the  liquid  thicker.  When  its  temperature 
reaches  220°,  we  can  turn  the  flask  upside  down  and  the  sulphur 
scarcely  runs  on  the  sides.  At  about  260°  it  again  becomes 
liquid,  and  at  448°  it  boils,  forming  a  red  vapor.  We  now 
pour  it  into  cold  water,  moving  the  flask  so  that  all  does  not 
fall  in  the  same  place.  On  taking  the  sulphur  from  the  water, 
we  find  that  its  properties  are  much  changed :  it  is  transparent 
and  very  elastic ;  we  pull  it  out  in  long  threads.  This  curious 
form,  which  is  called  soft  sulphur,  is  due  to  a  molecular  condition 


SULPHIDES. — HYDROGEN    SULPHIDE.  75 

of  the  element ;  we  must  believe  that  its  molecules  contain  more 
energy  than  those  of  ordinary  sulphur,  for  if  we  gradually  heat  it, 
it  at  once  becomes  opaque  and  brittle,  and  at  the  same  time  much 
hotter  than  we  have  heated  it.  It  changes  spontaneously  in  this 
manner  after  we  have  kept  it  a  few  hours.  Soft  sulphur  is 
amorphous  ;  that  is,  has  no  crystalline  form. 

Besides  these  two  forms  of  sulphur,  prismatic  crystals  and 
soft  sulphur,  there  is  another.  Native  sulphur  is  crystallized 
in  orthorhombic  forms,  generally  pyramids  modified  by  other 
forms,  and  the  crystals  obtained  from  solutions  in  carbon  di- 
sulphide  belong  to  the  same  system.  The  monoclinic  needles 
in  our  crucible  also  gradually  change  into  this  form :  upon 
standing  they  become  opaque  and  brittle  owing  to  a  rearrange- 
ment of  the  molecules. 

Because  sulphur  has  two  distinct  crystalline  forms,  it  is  said 
to  be  dimorphous.  The  density  of  prismatic  sulphur  is  1.96; 
that  of  octahedral  sulphur  is  2.05.  At  high  temperatures 
the  vapor  density  of  sulphur  is  nearly  32,  which  corresponds  to 
the  formula  S2. 

96.  Sulphur  takes  fire  in  the  air  at  a  temperature  below  red- 
ness :  its  combustion  is  its  union  with  oxygen,  forming  sulphur 
dioxide,  SO2,  called  also  sulphurous  oxide  and  sulphurous  acid 
gas.     By  the  aid  of  heat,  sulphur  unites  directly  with  many  other 
elements  :  we  have  seen  in  one  of  our  experiments  (§  4)  that  cop- 
per burns  brilliantly  in  sulphur  vapor,  and  in  the  same  manner  we 
might  burn  some  iron  wire,  forming  iron  sulphide. 

Sulphur  is  used  in  the  manufacture  of  matches,  gunpowder, 
sulphuric  acid,  and  many  other  operations. 

97.  Sulphides. — We  put  a  little  antimony  sulphide  into  a  test- 
tube,  and  boil  it  with  some  hydrochloric  acid.     A  gas  having  the 
unpleasant  odor  of  rotten  eggs  is  given  off,  and  antimony  chloride 
remains  in  the  tube.    This  gas,  which  we  shall  now  study,  is  called 
hydrogen  sulphide,  or  sulphuretted  hydrogen ;  nearly  all  the  sul- 
phides form  this  gas  when  boiled  with  hydrochloric  acid,  and  the 
reaction  gives  us  a  test  for  the  sulphides. 

98.  Hydrogen  Sulphide,  H2S. — Into  a  bottle  like  that  which 


76 


LESSONS    IN    CHEMISTRY. 


served  for  the  preparation  of  hydrogen,  we  put  some  ferrous  sul- 
phide, which  we  have  made  by  heating  to  redness  in  an  earthen 
crucible  a  mixture  of  iron  filings  with  about  its  own  weight  of 
sulphur.  We  then  pour  through  the  funnel-tube  some  dilute  sul- 
phuric acid,  and  at  once  or  in  a  few  minutes  an  effervescence  shows 
us  that  gas  is  being  given  off,  and  we  soon  detect  this  gas  by  its 
odor.  It  is  a  compound  of  hydrogen  and  sulphur,  and  is  formed 
by  the  reaction 

FeS  -f-         H2S04       -  H2S  +          FeSO4 

Ferrous  sulphide.        Sulphuric  acid.        Hydrogen  sulphide.        Ferrous  sulphate. 

The  ferrous  sulphate  formed  remains  dissolved  in  the  water. 

As  we  often  desire  this  gas  in  the  laboratory,  we  sometimes 
employ  a  self-regulating  apparatus  consisting  of  two  bottles  which 

have  openings  near  the 
bottom,  and  these  open- 
ings are  connected  by  a 
stout  rubber  tube  (Fig. 
43).  In  one  we  put  a 
layer  of  clean  pebbles 
that  rise  above  the  lower 
opening,  and  on  this  the 
ferrous  sulphide ;  to  the 
neck  of  this  bottle  we 
adapt  a  glass  stop-cock  by 
the  aid  of  a  good  cork. 
In  the  other  bottle,  which 
we  must  not  cork,  we  pour  our  dilute  sulphuric  acid.  When  we 
open  the  stop-cock,  the  acid  runs  in  on  the  ferrous  sulphide;  the 
gas  is  then  formed,  and  we  may  keep  it  in  the  bottle  or  use  it  as 
we  desire :  when  we  close  the  stop-cock,  the  gas  forming  in  the 
bottle  forces  the  acid  into  the  other  bottle,  and  as  soon  as  the  sur- 
face of  the  acid  is  below  the  top  of  the  layer  of  pebbles,  the  fer- 
rous sulphide  is  no  longer  acted  on.  We  may  use  this  apparatus 
for  the  preparation  of  hydrogen  and  carbon  dioxide  (§  234),  of 
course  cleaning  it  out  before  changing  the  materials. 

99.  PROPERTIES. — Hydrogen  sulphide  is  a  colorless  gas,  having 


FIG.  43. 


HYDROGEN    SULPHIDE.  77 

a  stinking  and  penetrating  odor.  Its  density  being  17  times  that 
of  hydrogen  or  17  X  .0693  that  of  the  air,  its  molecular  weight 
must  be  34  (§  48).  By  strong  pressure  it  is  converted  into  a  color- 
less liquid.  At  ordinary  temperatures  water  dissolves  about  three 
times  its  volume  of  hydrogen  sulphide,  and  the  solution  is  some- 
times used  in  the  laboratory,  but  it  does  not  keep  long,  for  the  air 
oxidizes  the  hydrogen,  forming  water,  while  sulphur  is  deposited. 

We  can  easily  determine  the  composition  of  this  gas.  Into  a  long  test-tube 
of  hard  glass  we  thrust  a  roll  of  tin  foil,  and  fill  the  tube  with  hydrogen  sul- 
phide 5  after  tightly  corking  the  tube,  we  heat  it  until  the  tin  acquires  a  yel- 
low color.  After  the  tube  has  cooled,  we  uncork  it  under  the  surface  of  mer- 
cury, and  we  find  that  the  volume  of  gas  has  not  changed.  The  remaining 
gas  is  hydrogen,  and  two  volumes  (one  molecule)  of  hydrogen  sulphide  there- 
fore contain  two  volumes  (two  atoms)  of  hydrogen.  Subtracting,  now,  the 
molecular  weight  of  hydrogen  from  that  of  hydrogen  sulphide,  we  have  34  —  2 
=  32,  the  amount  of  sulphur  in  one  molecule,  and  this  we  know  represents 
half  a  molecule  or  one  atom  of  that  element.  The  formula  of  the  gas  is 
therefore  H2S. 

Hydrogen  sulphide  is  a  combustible  gas,  as  we  can  easily  under- 
stand, since  its  molecule  contains  only  hydrogen  and  sulphur,  both 
of  which  are  able  to  unite  with  the  oxygen  of  the  air,  the  first  to 
form  water,  and  the  second  to  form  sulphur  dioxide,  the  same  gas 
which  is  formed  when  sulphur  burns  in  the  air.  When  we  light 
the  gas  at  the  end  of  the  delivery-tube,  it  burns  with  a  blue  flame. 

100.  Certain  reactions  of  this  gas  make  it  exceedingly  valuable 
in  the  laboratory.  We  pass  the  delivery-tube  from  our  apparatus 
into  a  solution  of  copper  sulphate  in  water :  a  brownish-black  pre- 
cipitate is  formed  as  soon  as  the  gas  comes  in  contact  with  the 
liquid.  This  is  copper  sulphide,  and  sulphuric  acid  remains  in  the 
solution. 

CuSO*       +        H2S  CuS  +  H2SO* 

Copper  sulphate.  Copper  sulphide.          Sulphuric  acid. 

We  pass  the  gas  into  a  solution  of  antimony  chloride,  and  an 
orange-colored  precipitate  of  antimony  sulphide  forms,  while  hydro- 
chloric acid  is  in  the  liquid. 

2SbCl3         +         3H2S         =  Sb2S3         +         6HC1 

Antimony  chloride.  Antimony  sulphide. 

In  a  solution  of  zinc  acetate,  we  would  have  thrown  down  a 
white  precipitate  of  zinc  sulphide.  Naturally,  in  these  reactions 


78  LESSONS   IN   CHEMISTRY. 

we  must  know  by  analysis  the  composition  of  the  molecules  which 
react  together,  and  that  of  the  bodies  which  are  formed,  before  we 
can  write  the  equations.  The  solutions  of  many  other  metallic 
compounds  are  decomposed  in  this  manner  by  hydrogen  sulphide, 
and  the  color  and  other  properties  of  the  metallic  sulphide  formed 
show  us  what  metal  exists  in  the  solution  to  which  we  apply  the 
test. 

Hydrogen  sulphide  is  at  once  decomposed  by  chlorine,  hydro- 
chloric acid  being  set  free. 

H2S  +  Cl2  =  2HC1  +  S 

Hydrogen  sulphide  is  a  poisonous  gas,  and  must  not  be  inhaled 
for  any  length  of  time,  even  when  very  much  diluted  with  air. 

101.  Hydrosulphides. — We  have  seen  that  hydroxides  are  formed  by  the 
action  of  water  on  the  oxides  (§  62),  and  that  these  hydroxides  contain  the 
group  of  atoms  OH,  which  we  call  hydroxyl.  On  examining  the  composi- 
tion of  the  molecule  of  hydrogen  sulphide,  we  see  that  it  is  analogous  to  that 
of  water,  but  contains  a  sulphur  atom  instead  of  an  oxygen  atom. 
HOH  HSH 

Water.  Hydrogen  sulphide. 

There  are  also  compounds  analogous  to  the  hydroxides,  but  containing  sul- 
phur instead  of  oxygen,  and  they  are  called  hydrosulphides.  We  pass  hydro- 
gen sulphide  into  a  solution  of  potassium  hydroxide;  it  is  absorbed,  and  a 
chemical  reaction  which  takes  place  causes  the  liquid  to  become  warm. 

KOH  +          HSH  KSH  +     HOH 

Potassium  hydroxide.    Hydrogen  sulphide.    Potassium  hydrosulphide.      Water. 

We  cannot  fail  to  notice  the  similarity  between  the  structure  of  these  mole- 
cules, and  this  similarity  leads  us  to  the  conclusion  that  as  far  as  combining 
with  atoms  of  hydrogen  and  potassium  is  concerned,  there  must  be  a  resem- 
blance between  sulphur  atoms  and  oxygen  atoms.  We  will  in  time  notice  that 
this  resemblance  does  not  stop  here,  but  is  borne  out  in  the  structure  of  many 
other  molecules  containing  sulphur  and  oxygen  atoms.  Since  one  atom  of 
sulphur  or  one  of  oxygen  is  capable  of  combining  with  two  atoms  of  hydrogen 
or  one  of  hydrogen  and  one  of  potassium,  and  since  we  take  the  hydrogen 
atom  as  the  unit  of  the  combining  power,  we  say  that  the  hydrogen  and 
potassium  atoms  are  monatomic  or  univalent,  and  that  the  oxygen  and 
sulphur  atoms  in  these  compounds  are  diatomic  or  bivalent. 


SULPHUR   DIOXIDE.  79 

LESSON    XII. 
SULPHUR   DIOXIDE.— SULPHUR   TRIOXIDB. 

102.  Sulphur  Dioxide,  SO2. — This  compound  is  formed  when 
sulphur  burns  in  the  air  or  in  oxygen :  we  could  not  obtain  it 
pure  by  burning  sulphur  in  air,  for  it  would  then  be  mixed  with 
the  other  constituents  of  the  air.     We  usually  prepare  the  gas  by 
boiling  sulphuric  acid  with  copper  clippings :  the  products  of  the 
operation  are  cupric  sulphate,  water,  and  sulphur  dioxide :  know- 
ing this,  we  may  write  our  equation, 

Cu       +        2H2S04      =         CuSO4          +  2H2Q      +      SO2 

Copper.          Sulphuric  acid.        Cupric  sulphate.  Sulphur  dioxide. 

We  conduct  the  experiment  in  an  apparatus  like  that  in  which 
we  prepared  chlorine,  and  if  we  desire  to  collect  the  gas  we  do  so 
by  downward  dry  displacement. 

103.  PROPERTIES. — Sulphur  dioxide  is  a  colorless,  suffocating 
gas.     Its  density  compared  to  hydrogen  is  32,  agreeing  with  that 
which  our  theory  should  indicate  (§  48),  and  it  is  therefore  a 
little  more  than  twice  as  heavy  as  an  equal  volume  of  air.  Under 
a  pressure  of  about  three  atmospheres,  or  at  a  temperature  of  — 8°, 
sulphur  dioxide  is  converted  into  a  colorless  liquid.     This  liquid 
is  readily  obtained  by  passing  the  gas  into  a  tube  surrounded  by 
a  mixture  of  ice  and  salt.     The  liquid  boils  at  — 8°,  and  when  its 
evaporation  is  aided  by  reducing  the  pressure,  much  lower  tem- 
peratures are  obtained.     We  can  easily  freeze  some  water  in  a 
test-tube  by  wrapping  the  lower  end  of  the  tube  in  cotton  wool, 
and  pouring  on  this  a  little  of  the  liquid  dioxide.     In  certain 
machines   for    making   ice,    the    cold   is   produced    by   rapidly 
evaporating    the    liquid    sulphur    dioxide    with    the    aid    of 
pumps. 

At  ordinary  temperatures  water  dissolves  about  forty  times  its 
volume  of  sulphurous  oxide,  and  the  solution  is  frequently  em- 
ployed in  the  laboratory. 


80  LESSONS    IN    CHEMISTRY. 

104.  Sulphurous  oxide  is  naturally  not   combustible,  for   the 
sulphur  which  it  contains  has  had   an   opportunity  to  combine 
with  all  of  the  oxygen   with  which  it  would  unite.     It  extin- 
guishes burning  bodies. 

While,  however,  one  atom  of  sulphur  will  not  combine  directly 
with  more  than  two  atoms  of  oxygen,  sulphurous  oxide  can  be 
still  further  oxidized  by  certain  reactions.  If  it  be  mixed  with 
oxygen,  and  the  mixture  passed  through  a  red-hot  tube  containing 
platinum  sponge,  the  two  gases  combine,  forming  sulphur  trioxide, 
SO3 ;  the  vapor  of  this  substance  may  be  condensed  by  passing  it 
into  an  ice-cold  receiver.  By  the  action  of  nitric  acid,  sulphur 
dioxide  is  converted  into  sulphuric  acid,  and  the  reaction  is  applied 
in  the  manufacture  of  the  latter  acid. 

In  a  tall  jar  we  dissolve  some  potassium  permanganate  in  water ; 
this  body  contains  a  large  proportion  of  oxygen,  with  which  it 
parts  easily  to  oxidizable  matters.  We  pass  some  sulphur  dioxide 
through  the  purple  solution,  which  is  rapidly  decolorized;  the 
sulphur  dioxide  becomes  sulphuric  acid  in  this  reaction,  and 
the  potassium  permanganate  is  said  to  be  reduced.  We  use  the 
term  reduction  to  mean  taking  away  oxygen,  and  any  body  which 
is  capable  of  removing  oxygen  from  other  substances  is  called  a 
reducing  agent. 

Sulphur  dioxide  is  used  for  bleaching  wool,  straw,  and  other 
matters  which  would  be  injured  by  chlorine.  The  substances  are 
bleached  by  being  put  in  a  room  in  which  sulphur  is  burned.  We 
may  in  this  manner  bleach  a  flower  in  a  bell-jar  under  which  some 
sulphur  is  burning. 

105.  Sulphites. — When  sulphur  dioxide  dissolves  in  water,  the  two  sub- 
stances really  combine,  and,  by  a  reaction  analogous  to  that  which  formed 
hypochlorous  acid,  sulphurous  acid  is  formed.     In  this  case,  however,  the  two 
atoms  of  hydrogen  exist  in  one  molecule  of  the  resulting  acid. 

SO*  +        H2Q      =  H2S03 

Sulphur  dioxide.  Sulphurous  acid. 

Sulphurous  acid  is  not  a  stable  compound ;  it  is  decomposed  when  we  try  to 
separate  it  from  its  solution,  and  yields  again  sulphur  dioxide  and  water. 
However,  both  of  the  hydrogen  atoms  are  replaceable  by  metal,  forming  salts 
which  are  called  sulphites;  by  passing  sulphur  dioxide  into  a  solution  of  so- 
dium hydroxide,  sodium  sulphite  and  water  are  formed. 


SULPHUR    TRIOXIDE.  81 


2NaOH         +        SO2        =        Na2S03        +         H20 
Sodium  hydroxide.  Sodium  sulphite. 

To  a  little  of  this  sodium  sulphite  in  a  test-tube  we  add  hydrochloric  acid; 
we  can  at  once  detect  the  pungent  odor  of  sulphur  dioxide,  and  a  solution  of 
common  salt  remains  in  the  tube. 

Na2S03  +  2HC1  =  SO2  +  H20  •:-  2NaCl 
This  gives  us  a  test  by  which  we  may  recognize  a  sulphite. 

106.  When  a  sulphite  is  boiled  with  sulphur,  the  latter  is  dissolved,  and  a 
compound  called  a  thiosulphate,  or  formerly  named  hyposulphite,  results 
With  sodium  sulphite,  we  would  have  sodium  thiosulphate. 

Na2S03  +  S          =         Na2S203  or  Na2S03S 

Sodium  sulphite.  Sodium  thiosulphate. 

It  will  be  noticed  that  the  thiosulphate  has  exactly  the  composition  of  a 
sulphate  ($  113)  in  which  an  atom  of  oxygen  in  replaced  by  an  atom  of  sul- 
phur. When  a  thiosulphate  is  treated  with  an  acid,  sulphur  dioxide  is 
evolved,  and  sulphur  separates.  The  rags  used  in  the  manufacture  of  paper 
are  bleached  by  chlorine,  but  no  chlorine  must  be  left  in  the  paper,  or  this 
would  be  injured.  In  presence  of  water,  sulphur  dioxide  (we  may  then  say 
sulphurous  acid)  and  chlorine  react  to  form  sulphuric  and  hydrochloric  acids, 
both  of  which  may  readily  be  neutralized. 

H2S03        +        Cl2      +      H20        =         H2S04        +        2HC1 
Sulphurous  acid.  Sulphuric  acid. 

Sodium  thiosulphate  therefore  serves  as  an  antichlor  in  the  manufacture  of 
paper. 

107.  Sulphur  Trioxide,  SO3.  —  We  have  seen  that  this  com- 
pound is  formed  by  the  direct  union  of  sulphur  dioxide  and  oxy-  I) 
gen  in  presence  of  heated  plaunum  sponge  (§  104)  :  other  porous  ' 
substances  cause  the  same  combination.  Sulphur  trioxide  is  usu- 
ally prepared  by  heating  fuming  sulphuric  acid,  which  is  some- 
times called  Nordhausen  acid^  because  it  was  for  a  time  manufac- 
tured only  in  the  village  of  Nordhausen,  in  the  Hartz,  by  distilling 
partially-dried  ferrous  sulphate.  It  contains  a  compound  of 
sulphur  trioxide  and  sulphuric  acid  ;  H2SO*  -f  SO3  ±=  H2S707. 
When  this  is  heated,  it  decomposes  into  its  constituents  ;  the 
sulphur  trioxide,  being  the  most  volatile,  is  condensed  in  cold 
flasks,  which  are  at  once  hermetically  sealed. 

Sulphur  trioxide  is  a  snowy-white  solid,  crystallizing  in  feather- 
like  flakes.     It   combines  so  energetically  with  water  that  each 
particle  makes  a  hissing  noise  like  hot  iron  on  touching  the  liquid. 
The  result  of  this  combination  is  sulphuric  acid. 
SO3  +  H20  =  H2SO* 


82  LESSONS   IN    CHEMISTRY. 

LESSON    XIII. 
SULPHURIC  ACID,  H2SO*. 

108.  Into  a  jar  of  oxygen  containing  a  little  water,  we  lower  a 
deflagrating-spoon  containing  burning  sulphur.  The  jar  soon  be- 
comes filled  with  sulphur  dioxide,  and  when  the  flame  of  the  sul- 
phur is  extinguished,  we  pour  into  the  jar  a  little  nitric  acid.  Red 
vapors  at  once  become  apparent,  but  disappear  in  a  little  while : 
in  order  to  mix  the  gases  well,  we  now  shake  the  jar,  keeping  jt 
closely  covered,  and  then  by  means  of  a  long  glass  tube  we  blow 
some  air  into  it :  red  vapors  are  again  produced.  It  is  evident 
that  some  chemical  change  has  occurred  between  the  nitric  acid 
and  sulphur  dioxide,  and  that  another  change  takes  place  between 
the  gases  in  the  jar  and  the  air  which  we  have  introduced.  The 
first  change  is  the  production  of  sulphuric  acid,  and  the  conversion 
of  the  nitric  acid  into  the  red  vapors  of  nitrogen  peroxide.  Since 
one  molecule  of  nitric  acid  contains  only  one  atom  of  hydrogen, 
while  one  molecule  of  sulphuric  acid  contains  two  such  atoms,  two 
molecules  of  nitric  acid  must  react  with  one  of  sulphur  dioxide. 

SO2  +     2HN03     =         H2SO*         +         2N02 

Nitric  acid.        Sulphuric  acid.          Red  vapors. 

The  red  vapors  react  with  the  water  in  the  jar  and  more  of  the 
sulphur  dioxide,  converting  the  latter  into  sulphuric  acid. 

SO2  +  NO2  +  H20  =  H2SO*  +  NO  - 

Nitric  oxide. 

But  the  nitric  oxide,  which  is  a  colorless  gas,  is  not  lost :  it 
takes  an  atom  of  oxygen  from  the  air  blown  into  the  jar,  and 
again  forms  red  vapors. 

NO  +  0  =  NO2 

These  red  vapors  in  turn  react  with  water  and  more  sulphur 
dioxide,  and  this  series  of  reactions  continues  until  all  of  the 
sulphur  dioxide  is  converted  into  sulphuric  acid.  Thus,  a  small 
quantity  of  the  oxides  of  nitrogen  will  effect  the  conversion  of 


SULPHURIC   ACID.  83 

a  large  quantity  of  sulphur  dioxide  into   sulphuric  acid,  the 
oxygen  needed  being  taken  from  the  air. 

109.  These  reactions  are  those  which  actually  take  place  in  the 
manufacture  of  sulphuric  acid,  which  is  commonly  called  oil  of 
vitriol,  and  of  which  enormous  quantities  are  used  at  one  stage  or 
another  in  the  manufacture  of  nearly  all  other  chemical  com- 
pounds.    The  sulphur  dioxide  is  obtained  by  burning  sulphur  in 
furnaces  (A A,  Fig.  44),  the  heat  of  which  boils  water  for  the 
steam  required  in  the  operation.      The  sulphur  dioxide  formed 
passes  through  a  series  of  leaden  chambers,  in  one  of  which  (D) 
it  comes  in  contact  with  nitric  acid,  which  trickles  down  over  a 
sort  of  cascade  (EE).     The  gases  then  pass  through  other  leaden 
chambers  into  which  steam  is  injected  (HH)  :  a  further  amount 
of  sulphuric  acid  is  produced,  and  this  collects  on  the  floor 
of  the  chambers,  from  which  it  is  drawn  off.    An  excess  of  air 
must  be  passed  into  the  chambers  in  order  to  reoxidize  the 
nitric  oxide,  and  as  the  nitrogen  of  the  air  which  must  be  allowed 
to  escape  from  the  apparatus  would  carry  off  some  of  that  oxide 
of  nitrogen,  all  the  waste  gases  are  obliged  to  pass  through  a 
tower  (R)  filled  with  coke  which  is  kept  wet  with  strong  sulphuric 
acid.     This  latter  absorbs  the  nitrous  gases,  and  as  it  runs  from 
the  tower  is  conducted  into  a  vessel  (i)t  from  which  it  may  be 
forced  by  steam  pressure  to  the  top  of  the  first  small  chamber  (C)-, 
through  which  the  sulphur  dioxide  is  caused  to  pass.     Here  the 
sulphur  dioxide  removes  all  of  the  nitrous  gases  and  carries  them 
again  into  the  chambers,  so  that  only  nitrogen  from  the  air  used 
escapes  at  the  chimney  of  the  coke  column.     The  chambers  are 
of  various  sizes,  sometimes  five  metres  wide  and  high,  and  ten, 
twenty,  or  even  more  metres  in  length. 

The  acid  drawn  from  the  leaden  chambers  is  called  chamber 
acid:  it  is  strong  enough  for  many  purposes,  its  density  being 
1.5.  The  strong  acid,  density  1.842,  is  made  by  evaporating 
the  chamber  acid  in  leaden  boilers  until  its  further  concentration 
would  dissolve  the  lead ;  it  is  then  transferred  to  expensive  plati- 
num stills,  where  the  evaporation  is  terminated. 

110.  The  sulphuric  acid  of  commerce  always  contains  a  little- 


LESSONS    IN    CHEMISTRY. 


SULPHURIC    ACID.  85 

lead  sulphate,  formed  in  the  chambers  and  evaporating  boilers, 
and  when  it  is  diluted  with  water  this  lead  sulphate  becomes  in- 
soluble and  separates  as  a  white  precipitate.  It  is  often  brown 
from  the  presence  of  a  little  carbonaceous  matter.  Sometimes  the 
sulphur  dioxide  is  obtained  by  burning  iron  pyrites  (iron  disul- 
phide),  and,  as  the  pyrites  often  contains  arsenic,  the  resulting  sul- 
phuric acid  also  contains  arsenic.  Pure  sulphuric  acid  is  made 
by  distilling  the  commercial  acid  in  glass  retorts ;  the  operation 
requires  great  care,  for  the  retorts  sometimes  break,  and  the  vapors 
of  the  sulphuric  acid  are  most  corrosive  and  suffocating. 

111.  Properties. — Pure  sulphuric  acid  is  a  colorless,  oily  liquid, 
having  at  12°  a  density  of  1.842.  It  solidifies  at  10.5°,  and  boils 
at  about  338°  :  its  boiling  is  accompanied  by  explosive  emission  of 
vapor,  which  may  be  obviated  by  putting  some  pieces  of  platinum 
in  the  vessel.  Sulphuric  acid  is  soluble  in  all  proportions  of  water, 
and  the  mixture  is  accompanied  by  the  production  of  great  heat, 
showing  that  there  is  a  true  chemical  combination  between  the 
water  and  acid.  In  diluting  sulphuric  acid  with  water,  we  always 
pour  the  acid  very  gradually  into  the  water,  which  we  stir  con- 
stantly. If  the  mixture  is  made  suddenly,  part  of  the  acid  is 
sometimes  thrown  out  of  the  vessel. 

The  affinity  of  sulphuric  acid  for  water  is  so  strong,  that  the 
acid  causes  the  formation  of  water  in  many  substances  which  do 
not  contain  water,  but  contain  hydrogen  and  oxygen  in  the  pro- 
portions required  for  its  formation.  In  a  beaker  glass,  or  other 
thin  glass  vessel,  we  pour  a  little  strong  solution  of  sugar,  and 
then  some  concentrated  sulphuric  acid  :  instantly  the  mixture  turns 
black,  and  a  mass  of  porous  charcoal  fills  the  vessel,  which  may 
overflow  if  we  have  used  too  much  of  the  materials.  Sugar  con- 
tains carbon  or  charcoal,  and  oxygen  and  hydrogen  in  the  propor= 
tions  to  form  water.  For  the  same  reason  a  chip  of  wood  with 
which  we  stir  some  sulphuric  acid  quickly  becomes  blackened,  and 
the  brown  color  which  the  acid  acquires  shows  us  why  the  common 
acid  is  often  brown. 

When  sulphuric  acid  is  passed  through  a  red-hot  tube,  it  is 
decomposed  into  sulphur  dioxide,  oxygen,  and  water. 


86  LESSONS    IN    CHEMISTRY. 

H2SO*        =        SO2        +         0         +        H20 

We  have  already  seen  how  zinc  acts  on  sulphuric  acid,  replacing 
the  hydrogen  which  then  becomes  free.  The  action  of  copper  on 
the  acid  is  a  reducing  action,  part  of  the  sulphuric  acid  being 
reduced  to  sulphur  dioxide. 

112.  Molecular  structure  of  sulphuric  acid. — We  have  seen  that  hypochlorous 
acid  contains  the  group  hydroxyl,  OH  ;  sulphuric  acid  also  contains  this  group, 
and  we  may  understand  the  structure  of  its  molecule  by  studying  some  simple 
reactions.  Since  a  molecule  of  sulphur  dioxide  contains  two  atoms  of  oxygen, 
each  of  which  is  diatomic, — that  is,  capable  of  combining  with  two  atoms  of 
hydrogen, — the  sulphur  atom  must  in  this  compound  have  as  much  combining 
power  as  four  atoms  of  hydrogen  :  we  call  it  tetratomic.  Yet  this  sulphur  atom 
is  capable  of  combining  with  another  atom  of  oxygen ;  it  is  unsaturated  with 
oxygen,  although  it  is  satisfied  with  the  two  atoms.  We  mix  in  a  glass  jar 
equal  volumes  of  chlorine  and  sulphur  dioxide,  and  expose  the  mixture  to 
direct  sunlight :  the  gases  combine  to  form  a  colorless  liquid,  having  a  suffo- 
cating vapor,  and  we  call  the  compound  sulphuryl  chloride.  Analysis  shows 
that  it  contains  S02C12,  and  for  convenience'  sake  the  group  of  atoms  SO2  is 
called  sulphuryl.  Each  atom  of  chlorine  is  worth  one  of  hydrogen,  and  if 
in  sulphur  dioxide  the  sulphur  atom  is  tetratomic,  it  must  be  hexatomic  in 
sulphuryl  chloride.  We  may  represent  this  relative  combining  capacity  by 
little  lines,  which  will  show  us,  not  how  and  where  the  atoms  unite,  but  the 
relative  worth  of  the  atoms  in  combination.  The  free  atom  of  hydrogen  or 
of  chlorine  would  be  indicated  to  be  monatomic  by  a  single  line,  thus,  H-,  C1-; 
and  in  the  molecules  of  these  two  elements  or  of  their  one  compound  a  single 
line  between  the  two  symbols  would  show  that  one  has  as  much  combining 
power  as  the  other  : 

H-H  C1-C1  H-C1 

The  symbol  of  a  diatomic  element  must  have  two  lines,  to  show  that  it  is 
worth  two  monatomic  atoms,  and  we  may  write  water  and  hydrogen  sulphide, 

H-O-H  H-S-H 

For  sulphur  dioxide,  sulphur  trioxide,  and  sulphuryl  chloride,  in  the  first 
of  which  the  sulphur  atom  is  tetratomic  and  in  the  other  two  hexatomic,  we 
must  show  the  combining  power,  or  atomicity,  as  it  is  often  called,  of  the 
elements  by  four  or  six  lines,  and  show  that  the  oxygen  is  diatomic  by  giving 
its  atoms  each  two  lines.  We  therefore  write, 

0=8=0  f1  °    ,? 

o=s=o  us" 

ci  6 

Sulphur  dioxide.  Sulphuryl  chloride.  Sulphur  trioxide. 

When  sulphuryl  chloride  is  poured  into  water,  both  substances  are  decom- 
posed, sulphuric  and  hydrochloric  acids  being  formed. 

S02C12        +        2H20  =  H2S04        +        2HC1 


SULPHATES.  87 

We  must  explain  this  reaction  by  a  replacement  of  the  chlorine  atoms  in  the 
sulphiiryl  chloride  by  other  atoms,  or  groups  of  atoms,  which  have  the  same 
combining  power,  and  we  would  then  conclude  that  sulphuric  acid  contains 
two  hydroxyl  groups,  and  we  might  call  it  sulphury  I  hydrate. 

0  0 

C1-S-C1     +     H-O-H     +     H-O-H     =     H-0-S-O-H     +     HC1     +     HC1 

o  6 

Sulphury  1  Water  (two  molecules).  Sulphuric  acid.  Hydrochloric  acid 

chloride.  (2  molecules.) 

Analogous  study  of  the  manner  in  which  compounds  are  formed  and  decom- 
posed, and  of  the  relative  worth  of  the  atoms,  has  led  chemists  to  hold  definite 
ideas  of  the  relations  which  the  atoms  bear  to  each  other  in  a  great  number 
of  molecules.  The  group  of  atoms  OH  is  called  a  compound  radical  because  it 
is  capable  of  replacing  an  atom  or  simple  radical.  In  the  same  manner  the 
group  SO2  is  a  radical,  as  in  general  are  all  groups  of  atoms  which  pass  by 
double  decomposition  and  without  change  from  one  molecule  to  another.  Some 
radicals,  like  SO2,  can  be  separated  and  studied,  because  the  combining  power 
of  the  atoms  in  them,  though  not  saturated,  is  satisfied ;  others,  like  -OH,  can- 
not be  separated,  because  their  atoms  are  not  satisfied  with  each  other.  Why 
this  is,  chemists  have  not  yet  been  able  to  explain  satisfactorily,  but  the  fact 
may  be  stated  that  a  monatomic  radical  cannot  usually  exist  except  in  com- 
bination :  this  applies  to  monatomic  atoms  as  well  as  to  monatomic  compound 
radicals ;  we  have  already  seen  that  the  molecules  of  hydrogen  and  chlorine 
must  each  contain  two  atoms. 

There  are  two  other  elements  whose  atoms  exactly  resemble  sulphur  in  their 
power  of  combining  with  other  atoms.  They  are  selenium  and  tellurium. 
They  are  found  only  in  small  quantities,  usually  associated  with  gold,  silver, 
and  copper  in  certain  ores  of  these  metals. 


LESSON    XIV, 
SULPHATES. 

113.  When  the  hydrogen  of  sulphuric  acid  is  replaced  by 
metals,  sulphates  are  formed,  but  as  there  are  two  atoms  of  hydro- 
gen, and  either  one  or  both  may  be  replaced,  we  can  understand 
that  there  may  be  two  kinds  of  sulphates.  If  only  one  hydrogen 
atom  be  replaced,  the  resulting  salt  will  have  acid  properties,  for 
it  still  contains  an  atom  of  replaceable  hydrogen  ;  but  if  both  be 
replaced,  we  have  a  neutral  salt, — that  is,  one  which  is  neither  acid 


88  LESSONS    IN    CHEMISTRY. 

nor  alkaline.  We  may  study  the  formation  of  two  of  these  salts 
in  the  reaction  of  one  and  two  molecules  of  sodium  hydroxide  with 
one  molecule  of  sulphuric  acid. 

H2SO*      +       NaOH        =        NaHSO4        +        WO 
Sodium  hydroxide.    Sodium  acid  sulphate, 

H2S04      +      2NaOH         =         Na2S04         +         2H2Q 
Sodium  sulphate. 

But  in  the  action  of  zinc  on  sulphuric  acid,  one  atom  of  zinc 
replaces  two  atoms  of  hydrogen.  In  the  same  manner,  if  we  boil 
sulphuric  acid  with  lead  oxide,  we  have  formed  lead  sulphate,  in 
which  one  atom  of  lead  replaces  both  atoms  of  hydrogen. 

PbO        +        H2SO*       =        PbSO*       +        H2Q 

Lead  oxide.  Lead  sulphate. 

Since  one  atom  of  zinc  or  one  of  lead  is  thus  capable  of  replacing 
two  atoms  of  hydrogen,  those  metals  are  said  to  be  diatomic ;  and 
since  sulphuric  acid  contains  two  atoms  of  hydrogen  which  may  be 
replaced  by  two  atoms  of  a  monatomic  metal,  like  sodium,  or  by  one 
atom  of  a  diatomic  metal,  like  zinc,  it  is  called  a  dibasic  acid,  and 
is  capable  of  forming  neutral  and  acid  salts. 

114.  With  the  exception  of  the  sulphates  of  barium,  strontium, 
and  lead,  all  the  sulphates  are  soluble  in  water,  but  calcium 
sulphate,   silver   sulphate,   and   mercurous   sulphate  are    only 
slightly  soluble. 

115.  To  a  solution  of  magnesium  sulphate  we  add  a  few  drops 
of  solution  of  barium  chloride  or  barium  nitrate.     A  white  cloud 
forms ;  this  is  insoluble  barium  sulphate ;  when  it  has  settled,  we 
may  pour  off  most  of  the  liquid,  and  we  will  find  that  our  white 
substance  is  not  dissolved  by  boiling  nitric  acid.    This  test  enables 
us  to  recognize  either  a  soluble  sulphate  or  uncombined  sulphuric 
acid. 

Some  of  the  sulphates  form  anhydrous  crystals, — that  is,  with 
out  water ;  others  contain  water  of  crystallization. 

116.  Sodium  Sulphate,  Na2S04,  was  for  a  long  time  called 
Glauber's  salt,   because  Glauber  found  that  it  was  useful  as  a 
purgative    medicine.      It    crystallizes    in    colorless,    monoclinic 
prisms  containing  ten  molecules  of  water  of  crystallization,  so  that 


SULPHATES.  89 

the  formula  of  the  crystals  is  Na2S04  +  10H20.  They  are  sol- 
uble in  about  ten  times  their  weight  of  water  at  0°,  and  in  one- 
third  their  weight  at  33°  ;  if  a  saturated  solution  be  made  at  the 
latter  temperature  and  immediately  sealed,  it  will  remain  liquid 
indefinitely,  but  on  opening  the  flask  the  whole  of  the  liquid  in- 
stantly becomes  a  mass  of  crystals. 

117.  Potassium  Sulphate,   K2S04.  forms  very  hard,  colorless 
crystals,  not  very  soluble  in  water ;  it  is  poisonous. 

118.  Calcium  Sulphate,  CaSO. — We  have  in  a  beaker  glass  a 
very  strong  solution  of  calcium  chloride.     To  this  we  add  at  arm's 
length  about  half  its  volume  of  concentrated  sulphuric  acid  :  the 
contents  of  the  beaker  at  once  become  so  solid  that  we  can  in- 
vert it  and  nothing  runs  out.     This  solid  is  calcium  sulphate. 

CaCl2        +        H2SO*        =        CaSO*        +        2HC1 
Calcium  chloride.  Calcium  sulphate. 

The  minerals  gypsum,  alabaster,  and  selenite  consist  of  cal- 
cium sulphate  combined  with  two  molecules  of  water  of 
crystallization ;  this  water  is  driven  out  when  they  are  heated  to 
120°,  leaving  the  anhydrous  sulphate  as  a  fine  white  powder, 
known  as  plaster  of  Paris.  Unless  it  has  been  heated  to  too  high 
a  temperature,  this  substance  will  again  combine  with  its  water  of 
crystallization,  and  such  combination  takes  place  when  plaster  of 
Paris  is  mixed  with  water.  Plaster  casts  are  made  by  mixing  the 
plaster  and  water  to  a  creamy  consistence,  and  pouring  the  liquid 
into  the  moulds :  in  a  few  minutes  the  plaster  sets,  or  becomes 
hardened,  and  in  so  doing  it  expands  and  completely  fills  the 
mould.  Calcium  sulphate  dissolves  in  about  500  times  its  weight 
of  water.  It  is  a  valuable  fertilizer  for  certain  soils. 

119.  Strontium  Sulphate,  SrSO,  constitutes  the  mineral  celes- 
tite,  so  called  because  it  often  has  a  blue  color,  though  the  pure  salt 
is  white.    It  is  insoluble  in  water,  and  is  precipitated  when  a  soluble 
strontium  salt  is  added  to  sulphuric  acid  or  a  soluble  sulphate. 

120.  Barium  Sulphate,  BaSO4,  is  found  native  as  heavy  spar. 
We  have  seen  that  it  is  formed  by  the  reaction  of  sulphuric  acid 
with  soluble  salts  of  barium.    It  is  sometimes  used  for  adulterating 
white  lead  (§  250). 


90  LESSONS    IN   CHEMISTRY. 

121.  Magnesium  Sulphate,  MgSO4  -f  7H20,  is  commonly 
known  as  Epsom  salts.     It  is  made  by  dissolving  magnesium  car- 
bonate in  dilute  sulphuric  acid,  and  when  the  concentrated  solu- 
tion is  allowed  to  evaporate,  the  salt  separates  in  crystals  containing 
seven  molecules  of  water.     It  has  a  salty,  bitter,  and  unpleasant 
taste.     It  dissolves  in  about  three  times  its  weight  of  water.    It  is 
used  in  medicine. 

122.  Zinc  Sulphate,   ZnSO4  -f  7H20.— We  evaporate  to    a 
small  volume  the  liquid  remaining  in  the  bottle  in  which  we  made 
hydrogen  by  the  action  of  sulphuric  acid  on  zinc,  and  then  set  it 
aside  in  a  cool  place.      After  a  time  zinc  sulphate  separates  in 
beautiful  transparent  crystals,  containing  seven  molecules  of  water, 
and  of  exactly  the  same  form  as  those  of  magnesium  sulphate 
prepared  in  the  same  manner.     Compounds  which  have  in  their 
molecules  the  same  number  of  atoms  arranged  in  the  same  man- 
ner, usually  crystallize  in  the  same  form,  and  are  said  to  be  iso- 
morphous.     Zinc  sulphate  is  sometimes  called  white  vitriol.     It 
is  quite  soluble  in  water,  and  when  swallowed  it  acts  as  a  violent 
emetic. 

123.  Ferrous  Sulphate,  FeSO4  +  7H20.— This  salt,  called 
also  green   vitriol  and  copperas,  is  made  by  treating  scrap  iron 
with  dilute  sulphuric  acid;  hydrogen  is  disengaged,  just  as  in  the 
action  of  the  same  acid  on  zinc.     When  the  filtered  solution  is 
evaporated    and   set   aside   to    crystallize,    the   ferrous   sulphate 
separates  in  monoclinic  crystals  which  contain  seven  molecules 
of  water  of  crystallization.     These  crystals  are  pale  green  in 
color ;  when  exposed  to  dry  air,  they  lose  part  of  their  water 
of  crystallization,  and  the  surface  becomes  covered  with  a  white 
powder,  which  is  the  anhydrous  salt ;  they  are  said  to  effloresce. 
After  a  time  this  powder  becomes  yellow,  from  an  absorption  of 
oxygen  (§  527).    Ferrous  sulphate  is  soluble  in  less  than  twice  its 
weight  of  cold  water,  and  much  more  soluble  in  boiling  water. 
It  is  poisonous. 

124.  Cupric  Sulphate,  CuSO4  -f  5H20.— This  beautiful  blue 
salt,  often    called   blue  vitriol,  may  be  prepared  from  the  res- 
idue of  the  preparation  of  sulphur  dioxide  by  diluting  it  with 


NITROGEN. — THE   ATMOSPHERE.  91 

water,  filtering,  and  evaporating  to  crystallization.  It  is  usually 
made  by  roasting — that  is,  heating  in  the  air — copper  sulphide 
(§  484),  and  treating  the  mass  with  water.  When  the  blue  crys- 
tals are  heated,  the  water  is  driven  out,  and  the  white  anhydrous 
salt  is  left.  Cupric  sulphate  dissolves  in  four  times  its  weight  of 
cold,  or  twice  its  weight  of  boiling  water.  To  a  solution  of  this 
salt  we  add  a  little  ammonia  water ;  a  pale-blue  precipitate  forms, 
but  when  we  add  more  ammonia  this  precipitate  again  dissolves, 
and  a  deep-blue  liquid  is  obtained.  This  liquid  contains  ammo- 
niacal  cupric  sulphate.  Cupric  sulphate  is  used  in  telegraphic 
batteries,  in  dyeing,  for  electrotyping,  and  in  many  other  opera- 
tions. It  is  poisonous. 

125.  Lead  Sulphate,  PbSO4.— When  sulphuric  acid  or  the 
solution  of  a  sulphate  is  added  to  a  solution  containing  a  lead  salt, 
lead  sulphate  separates  as  a  white  precipitate.  It  occurs  in  nature 
as  the  mineral  anglesite.  It  is  insoluble  in  water,  but  dissolves 
in  strong  acids. 

Of  the  many  other  sulphates,  we  must  study  a  few  when  we 
shall  have  learned  some  of  the  peculiarities  of  the  corresponding 
metals. 


LESSON    XV. 
NITROGEN.— THE  ATMOSPHERE. 

126.  Nitrogen,  N  =  14. — On  the  water  in  the  pneumatic 
trough,  we  float  a  small  capsule  containing  a  little  sand  on  which 
we  have  placed  a  piece  of  phosphorus.  We  ignite  the  phos- 
phorus, and  place  over  it  a  bell-jar  which  may  rest  on  the  shelf 
in  the  trough  (Fig.  45).  At  first,  as  the  heat  of  the  burning 
phosphorus  expands  the  air,  a  few  bubbles  of  air  escape  under  the 
edge  of  the  jar,  but  this  soon  stops ;  presently  the  water  begins 
to  rise  in  the  jar,  and  the  phosphorus  no  longer  burns.  All 
the  oxygen  of  the  air  in  the  jar  has  been  consumed  by  the  phos- 
phorus, and  there  is  left  nitrogen,  with  which  the  oxygen  was 


92 


LESSONS    IN    CHEMISTRY. 


FlO.   45. 


mixed,  and  phosphoric  oxide.  The  latter  will  presently  dis- 
solve in  the  water,  and  we  may  then  examine  the  nitrogen, 
which  contains  but  very  small  quantities  of  other  gases. 

To  prepare  larger  quantities  of  nitrogen  free  from  most  of 
these  impurities,  we  pass  a  current  of 
air  through  a  tube  containing  pieces  of 
solid  potassium  hydroxide,  which  absorbs 
the  moisture  and  carbon  dioxide,  and 
then  through  a  long  tube  containing  red- 
hot  copper.  The  copper  combines  with 
the  oxygen,  forming  cupric  oxide,  and 
nitrogen  passes  out  at  the  end  of  the 
tube.  Perfectly  pure  nitrogen  can  be 
obtained  only  by  decomposing  certain 
compounds,  such  as  ammonium  nitrite. 
Upon  heating,  this  salt  yields  nitrogen 
and  water,  NH4N02  =  N2  -f  2H20. 

127.  Nitrogen  is  a  colorless,  tasteless,  and  odorless  gas.     Its 
density  compared  to  air  is  0.97,  or  compared  to  hydrogen,  14 ; 
as  its  atomic  weight  is  also  14,  its  molecule  must  contain  two 
atoms.     It  is  almost  insoluble  in  water,  and  difficult  to  liquefy. 
It  is  not  combustible,  neither  will  it  support  the  combustion  of 
other  substances.     It  combines  directly  with  only  a  few  of  the 
elements,  and  energy  is  absorbed  during  the  formation  of  many 
of  its  compounds ;  that  is,  the  nitrogen  atoms  have  a  stronger 
affinity  for  one  another  than  for  the  other  atoms  with  which 
they  are  combined. 

128.  The  Atmosphere. — The  chemical  composition  of  the  air 
was  first  determined  with  tolerable  accuracy  by  the  great  French 
chemist,  Lavoisier.    We  may  satisfy  ourselves  of  this  composition 
in  a  very  simple  manner.     Around  a  long  glass  tube,  closed  at 
one  end,  we  have  placed  four  caoutchouc  bands,  dividing  it  into 
five  equal  portions.     Into  this  tube,  which  must  be  perfectly  dry, 
we  drop  a  dry  piece  of  phosphorus,  and  tightly  cork  the  open 
end.     By  gently  heating  the  bottom  of  the  tube  over  a  lamp,  we 
inflame  the  phosphorus,  and  then  by  quickly  turning  the  tube 


THE    ATMOSPHERE. 


93 


bottom  up  and  giving  with  the  corked  end  a  few  sharp  blows  on 
the  table,  we  cause  the  burning  phosphorus  to  fall  the  whole 
length  of  the  tube.  If  our  experiment  has  been  well  made,  all 
the  oxygen  has  been  burned  from  the  air  in  the  tube,  which  we 
allow  to  cool,  and  then  carefully  uncork  with 
the  mouth  under  water.  As  soon  as  the  cork 
is  drawn,  the  water  rises  to  the  first  division 
(Fig.  46).  The  air  which  we  have  roughly 
analyzed,  then,  contained  about  one-fifth  oxy- 
gen and  four-fifths  nitrogen  by  volume. 

129.  A  very  accurate  analysis  of  air  is 
made  by  the  aid  of  the  eudiometer,  which  we 
have  studied.  Into  the  eudiometer  with  the 
caoutchouc  tube  and  plain  glass  tube,  which 
served  for  the  synthesis  of  water  (§  42),  but 
without  the  enclosing  wide  glass  tube,  we  in- 
troduce 100  measures  of  air  and  100  meas- 
ures of  pure  hydrogen.  After  adjusting  the 
mercury  level  in  the  two  tubes,  we  pass  an 
electric  spark :  at  once  the  oxygen  and  part 
of  the  hydrogen  are  converted  into  water, 
which  condenses,  and  the  volume  of  gas  is  re- 
duced. We  know  that  water  is  formed  by  the  union  of  two 
volumes  of  hydrogen  and  one  volume  of  oxygen  ;  consequently 
one- third  of  the  diminution  in  volume  must  be  caused  by  the 
removal  of  the  oxygen  of  the  100  measures  of  air.  On  again 
adjusting  the  level  of  the  mercury,  we  find  that  instead  of  200 
measures  we  have  only  137.21.  The  oxygen  present  in  100 

QAA  I  O1?   <?1 

measures  of  air  must,  then,  have  been   -  _,  or  20.93 

o 

measures.  We  conclude,  therefore,  that  100  volumes  of  air  con- 
tain 20.93  volumes  of  oxygen  and  79.07  volumes  of  nitrogen.* 
Since  oxygen  is  heavier  than  nitrogen,  these  relative  volumes 
will  not  express  the  relations  by  weight.  We  can  calculate  the 
weights  from  the  volumes,  and  the  result  would  show  us  that  76.87 
parts  by  weight  of  nitrogen  are  mixed  with  23.13  parts  of  oxygen. 


FIG.  46. 


*  This  nitrogen  contains  a  small  amount  of  argon  (g  130). 


94  LESSONS    IN    CHEMISTRY. 

These  proportions  are  confirmed  by  the  direct  analysis,  which  is  made  by 
passing  air  through  a  series  of  tubes  in  which  all  traces  of  carbon  dioxide 
and  moisture  are  absorbed :  thus  purified,  the  air  passes  through  a  tube  con- 
taining red-hot  copper  ($  127),  and  the  increase  in  weight  of  this  tube  gives 
the  amount  of  oxygen  in  the  air  analyzed.  The  nitrogen  passes  on  into  a 
glass  globe  in  which  a  vacuum  has  previously  been  made,  and  of  course  the 
increased  weight  of  this  globe  is  the  amount  of  nitrogen.  ' 

The  air  is  not  a  compound,  but  a  mixture,  and  we  may  expect 
that  the  proportions  of  the  constituents  shall  vary  a  little.  How- 
ever, the  composition  is  nearly  constant :  hundreds  of  analyses 
have  shown  that  the  proportion  of  oxygen  in  100  volumes  of 
unconfined  air  varies  only  from  20.86  to  21. 

130.  Argon, — The  nitrogen  remaining  after  the  absorption 
of  oxygen  from  purified  air  is  not  pure.     It  was  observed  quite 
recently  that  it  is  slightly  heavier  than  the  pure  nitrogen  ex- 
tracted from  chemical  compounds,  and  further  shown  that  this 
difference  in  density  is  due  to  a  hitherto  unknown  element,  to 
which  the  name  argon  has  been  given.     When  "  atmospheric" 
nitrogen  is  passed  over  heated  magnesium,  the  nitrogen  gradu- 
ally combines  with  the  metal,  and  a  small  volume  of  unabsorb- 
able  gas  remains.     This  has  a  density  of  19.9.     It  is  rather 
more  soluble  in  water  than  nitrogen,  and  has  been  reduced  to 
both  the  liquid  and  the  solid  states  at  very  low  temperatures. 
It  is  most  remarkable  for  its  entire  lack  of  chemical  affinities  : 
all  attempts  to  combine  it  with  other  elements  have  resulted 
negatively,  hence  the  name  (a'^oy,  inactive).     We  have  reason 
to  believe  that  each  molecule  consists  of  a  single  atom.     The 
atomic  weight,  therefore,  is  nearly  40. 

Careful  examination  of  liquefied  argon  has  led  to  the  discovery  of  four 
other  gaseous  elements  to  which  the  names  krypton,  neon,  metargon,  and  xenon 
have  been  given.  They  closely  resemble  argon  in  most  respects,  but  differ 
from  their  companion  in  their  densities  and  boiling  points. 

131.  We  pour  into  a  plate  some  clear  lime-water ;  in  a  few 
minutes  a  thin,  white  pellicle  forms  over  its  surface.     This  is  cal- 
cium carbonate,  and  has  been  formed  by  the  absorption  of  carbon 
dioxide  from  the  air.     Air  also  contains  more  or  less  vapor  of 
water,  which  is  deposited  in  the  form  of  dew  on  very  cold  objects. 


THE   ATMOSPHERE.  95 

The  proportions  of  vapor  of  water  and  carbon  dioxide  may  be  determined 
by  drawing  a  known  volume  of  air  through  a  series  of  tubes  (Fig.  47),  the 
first  of  which  contain  pumice-stone  and  sulphuric  acid,  and  the  others  frag- 
ments of  potassium  hydroxide.  The  increase  in  weight  of  the  first  tubes 
(D,  E,  F)  gives  the  weight  of  that  vapor,  and  the  increase  in  weight  of  the 
tubes  containing  potash  (A,  B,  C)  gives  us  the  proportion  of  carbon  dioxide. 
The  volume  of  air  which  contained  these  quantities  is  equal  to  the  volume  of 
water  which  runs  from  the  aspirator  (V).  We  can  calculate  the  weight  of  this 
air  from  its  volume,  for  at  0°  and  under  760  millimetres  barometric  pressure, 
one  litre  of  dry  air  weighs  1.2932  grammes. 

A  gas  expands  or  contracts  0.00366  of  its  volume  at  0°  for*  every  degree 
above  or  below  ^°,  and  since  the  volume  of  a  gas  is  inversely  as  the  pressure 
(Mariotte's  law),  the  volume  of  any  gas  may  be  calculated  for  0°  and  760  mil- 

Vh 
limetres  by  the  equation  V  =  760  /i  +  0  oo366t)  w^ere  ^  represents  the  volume 

at  t°,  and  h  the  barometric  pressure  expressed  in  millimetres. 

132.  The  quantity  of  vapor  of  water  which  the  air  can  take 
up  depends  on  the  temperature,  and  air  is  said  to  be .  saturated 
with  moisture  when  at  the  given  temperature  it  can  hold  no  more 
water  vapor.     It  is  then  said 
to  have  a  relative  humidity 
of  100 :    at  the  same  tem- 
perature half  that  quantity 
of  vapor  would  be  a  relative 
humidity  of  50.     But  if  the 
temperature     be     increased 
and  the  quantity  of  moist- 
ure   remain    the   same,   the 

relative  humidity  is  lowered,  "~FIO  47 

for  the  air  is  then  capable 

of  dissolving  more  vapor.  The  temperature  at  which  air  is 
completely  saturated  with  vapor  is  called  the  dew-point,  and 
this  may  be  determined  by  noting  the  temperature  at  which 
moisture  begins  to  deposit  on  the  walls  of  a  vessel  which  is 
artificially  cooled.  Substances  which  are  capable  of  absorbing 
moisture  from  the  atmosphere  are  said  to  be  hygroscopic.  Sul- 
phuric acid,  for  instance,  when  exposed  to  the  air  will  in  a  few 
days  take  up  enough  moisture  to  double  its  volume. 


96 


LESSONS    IN    CHEMISTRY. 


FIG.  48. 


133.  The  proportion  of  carbon  dioxide  present  in  the  air 
is  very  small :  it  is  about  three  parts  in  ten  thousand  of  air.  It 
is  thrown  into  the  atmosphere  from  volcanoes,  fissures  in  the  earth, 
and  mineral  springs,  but  the  largest  quantity  is  produced  by  com- 
bustion and  respiration.  It  does  not  accumulate  in  the  atmosphere, 
but  is  absorbed  by  plants,  and  under  the  influence  of  sunlight  is 
decomposed,  the  carbon  being  retained  for  the  growth  of  the  plant, 
while  oxygen  is  eliminated.  If  we  put  some  tender 
leaves,  water-cress  answers  very  well,  in  a  jar  which 
we  fill  with  water  charged  with  carbonic  acid, 
and  place  on  a  plate  so  that  the  water  may  not  run 
out,  and  then  expose  to  direct  sunlight,  in" a  short 
time  bubbles  of  gas  collect  in  the  jar  (Fig.  48). 
We  may  transfer  this  gas  to  a  small  tube,  and  if 
we  test  it  by  a  lighted  match,  we  find  that  it  is 
oxygen.  We  can  prove  that  carbon  dioxide  ex- 
ists in  the  air  exhaled  from  the  lungs,  by  blowing  the  breath  through 
lime-water  (Fig.  49),  which  quickly  becomes  clouded  by  the  for- 
mation of  calcium  carbonate.  In  the  same  manner,  if  we  burn  a 

lighted  taper  or  candle  in  a 
covered  jar,  and  then  pour  in 
some  lime-water,  and  shake 
the  jar,  the  milkiness  of  the 
water  shows  that  carbon  di- 
oxide has  been  formed. 

184.  Although  in  uncon- 
fined  air,  plants  and  vegetables 
remove  the  carbon  dioxide,  so 
that  its  proportion  does  not 
increase,  yet  if  the  air  be  con- 
fined, as  in  a  room  or  a  mine, 
this  gas  may  accumulate  to  as 
much  as  one  part  in  a  hundred 
49  of  air.  As  this  carbon  dioxide 

is  formed  at  the  expense  of 
the  oxygen  of  the  air,  the  proportion  of  oxygen  may  descend  as 


AMMONIA. 


97 


low  as  22  parts  per  hundred  by  weight,  instead  of  23.2.  At 
every  breath  a  man  consumes  about  4.87  per  cent,  of  the  oxygen 
which  he  inhales,  and  the  carbon  dioxide  exhaled  in  an  hour  is 
about  20  litres.  When  the  carbon  dioxide  in  the  air  is  pure, 
its  proportion  may  be  much  increased,  and  no  ill  effects  result ; 
but  in  addition  to  this  gas  a  considerable  proportion  of  animal 
matters  passes  from  the  lungs,  and,  together  with  that  thrown 
off  in  the  perspiration,  quickly  vitiates  the  atmosphere  of  an 
apartment  which  is  not  properly  ventilated. 

135.  Besides  the  substances  already  considered,  air  always  con- 
tains very  small  quantities  of  ammonia,  traces  of  nitric  acid,  and 
small  solid  particles  of  various  natures  which  are  carried  to  great 
distances  by  the  winds.  Sometimes  a  little  ozone  is  present,  and 
may  be  recognized  by  the  test  which  we  have  studied  (§  66). 


LESSON    XVI. 
AMMONIA  AND  ITS  COMPOUNDS. 

136.  Ammonia,  NH3. — In  a  glass  flask  to  which  we  have 
adapted  a  cork  and 
delivery-tube,  we  mix 
some  powdered  ammo- 
nium chloride  with  its 
own  weight  of  slaked 
lime.  We  then  fill 
the  rest  of  the  flask 
with  pieces  of  quick- 
lime, and  gently  heat 
it  on  a  sand-bath.  We 

soon  notice  the  pungent  -plG 

odor  of  the  gas  disen- 
gaged ;  as  this  gas  is  very  soluble  in  water,  we  cannot  collect  it 

7 


98 


LESSONS    IN    CHEMISTRY. 


over  that  liquid ;  we  may  collect  it  either  over  mercury  in  a 
small  pneumatic  trough,  or  by  upward  dry  displacement,  for  it  is 
lighter  than  air  (Fig.  50).  Slaked  lime  is  calcium  hydroxide, 
Ca(OH)2,  ammonium  chloride  is  a  compound  of  nitrogen,  hydro- 
gen, and  chlorine,  NH4C1.  We  may  write  the  reaction, 

2NH*C1         +         Ca(OH)2     =     2NR3       +         CaCl2       +      2H20 
Ammonium  chloride.  Lime.  Ammonia.       Calcium  chloride. 

The  calcium  chloride  formed  remains  in  the  flask,  and  the 
water  is  absorbed  by  the  pieces  of  lime  which  we  have  put  into 
the  flask  for  that  purpose.  We  could  not  dry  ammonia  gas  by 
passing  it  over  either  calcium  chloride  or  sulphuric  acid,  for  it 
combines  with  both  of  those  substances. 

137.  Properties. — The  ammonia  which  we  have  collected  is  a 
colorless  gas,  having  a  penetrating,  pungent  odor,  and  a  burning 
taste.  We  must  not  inhale  too  much  of  it,  for,  although  not 
poisonous,  it  often  produces  sudden  giddiness  or  vertigo.  Its 
density  compared  to  hydrogen  corresponds  with  half  its  molecular 

weight,  being  8.50 :  it  is  therefore  a 
little  more  than  half  as  heavy  as  air. 
By  strong  pressure,  it  is  readily  con- 
verted into  a  liquid,  and  this  liquid 
is  employed  in  some  forms  of  ice- 
machines,  where  it  produces  great  cold 
by  its  evaporation. 

Ammonia  is  very  soluble  in  water : 
at  0°  water  will  dissolve  1000  times 
its  volume  of  the  gas,  and  at  ordinary 
temperatures  about  700  times  its  vol- 
ume. We  have  fitted  to  a  glass  flask 
a  cork  through  which  passes  a  tube 
drawn  out  to  a  small  opening  on  the 
inside.  We  fill  this  flask  with  am- 
monia, by  dry  displacement,  and  after 
putting  in  the  cork  we  dip  the  end  of 
the  tube  into  a  vessel  of  water.  The  water  slowly  rises  in  the 
tube,  but  as  soon  as  it  reaches  the  narrow  end  the  ammonia  is 


FIG.  61. 


AMMONIA   AND    ITS   COMPOUNDS. 


99 


absorbed  so  rapidly  that  the  pressure  of  the  atmosphere  forces  the 
water  up  in  a  fountain  which  continues  until  all  of  the  ammonia 
is  dissolved  (Fig.  51).  The  solution  of  ammonia  in  water  is 
called  ammonia-water,  liquor  ammonise,  or  spirits  of  hartshorn. 
It  has  the  taste  and  odor  of  the  gas,  and  is  very  caustic.  When  it 
is  heated,  the  gas  is  driven  out,  and  we  may  most  readily  obtain 
ammonia  by  heating  strong  ammonia-water  in  a  flask,  and  drying 
the  gas  by  passing  it  through  a  tube  containing  quick-lime.  The 
strongest  ammonia-water  of  commerce  contains  about  35  per 
cent,  of  the  gas.  Its  density  is  about  0.882. 

138.  Ammonia  is  decomposed  into  nitrogen  and  hydrogen  by  very  high 
temperatures  or  by  the  continued  passage  of  electric  sparks.  Two  volumes  of 
ammonia  yield  four  volumes  of  the  mixed  gases,  and  if  we  mix  in  the  eudiom- 
eter these  four  volumes  with  one  and  a  half  volumes  of  oxygen  and  pass  the 
spark,  after  the  condensation  of  the  water  formed,  only  one  volume  of  gas  is 
left.  This  is  nitrogen,  and  two  volumes,  or  one  molecule,  of  ammonia  must 
therefore  contain  one  volume  (one  atom)  of  nitrogen,  and  three  volumes  (three 
atoms)  of  hydrogen. 

139.  Ammonia  is  combustible,  but  it  will  not  burn  in  the  air. 
We  may  cause  it  to  burn  at  a  jet  which  is  surrounded  by  oxygen, 
and  for  that  purpose  we  have  fitted  to  a 
short  wide  tube,  open  at  both  ends,  a  cork 
through  which  pass  two  tubes  (Fig.  52)  ; 
one  of  them  is  short  and  leads  oxygen 
from  a  gas-holder,  while  the  other  reaches 
nearly  to  the  top  of  the  wide  tube,  and 
conveys  ammonia  gas  from  a  small  flask 
in  which  we  boil  some  ammonia-water. 
As  soon  as  ammonia-gas  escapes  from 
the  jet,  we  turn  on  the  oxygen,  and  light 
the  ammonia,  which  burns  with  a  yellow 
flame,  forming  water  and  nitrogen. 

4NH3  +  302  =  6H20  +  2N2 
on,-  L       •  i  FIG.  52. 

Ihis  combustion  may  be  made  to  take 

place  more  slowly,  and  in  an  interesting  manner,  in  the  presence 
of  platinum.  Over  some  ammonia-water  contained  in  a  beaker 
glass  (Fig.  53)  we  suspend  a  coil  of  red-hot  platinum  wire,  so 


100 


LESSONS    IN    CHEMISTRY. 


FlG.  53. 


that  it  may  nearly  touch  the  liquid.  The  coil  will  continue  to 
glow  for  a  long  time  by  the  heat  evolved  from  the  slow  combustion 
of  the  ammonia  which  escapes  from  the  liquid 
and  mixes  with  the  oxygen  of  the  air.  If  now 
we  warm  the  beaker,  and  pass  bubbles  of  oxygen 
through  the  liquid,  each  bubble  causes  a  little 
explosion  as  it  combines  with  the  hydrogen  of 
the  ammonia.  Sometimes  the  beaker  becomes 
filled  with  white  fumes  of  ammonium  nitrite. 

140.  Ammonium  Compounds.  —  Ammonia  is 
not  the  only  compound  of  nitrogen  and  hydrogen.  Hydrazine 
and  Jiydrazoic  acid  are  the  names  of  two  remarkable  substances 
recently  discovered,  and  which  have  the  compositions  N2H*  and 
N3H  respectively. 

There  is  also  a  class  of  compounds  which  contain  more  than 
three  atoms  of  hydrogen  for  each  atom  of  nitrogen.  Over  a 
small  capsule  containing  some  warm  ammonia-water  we  have 
inverted  a  glass  jar,  and,  at  a  little  distance,  over  another  cap- 

sule  in  which  is  some 
warm  hydrochloric 
acid  we  have  inverted 
another  jar.  Each 
jar  now  contains  some 
of  the  gas  from  the 
liquid  under  it.  When 
we  raise  the  jars  and 
bring  their  mouths  to- 
gether, both  become  filled  with  dense  white  fumes  (Fig.  54). 
The  two  gases  have  combined,  and  a  body  called  ammonium  chlo- 
ride has  been  formed,  and  will  settle  on  the  sides  of  the  jars.  The 
combination  is  very  simply  expressed. 

NH3  +  HCl  =  NH4C1,  ammonium  chloride. 

We  see,  then,  that  while  the  nitrogen  atom  will  combine  with 
only  three  atoms  of  hydrogen  alone,  it  will  combine  with  four  if 
an  atom  of  chlorine  come  with  that  hydrogen.  In  the  same  man- 
ner, in  many  other  compounds  one  nitrogen  atom  is  combined  with 


-  54- 


AMMONIUM    CHLORIDE. 


101 


four  hydrogen  atoms,  and  one  other 'atom  or  group  of  atoms.  Nil4 
is  one  of  those  groups  of  atoms  which  we  call  radicals  (§  112)  ;  it 
passes  from  one  compound  to  another  without  change,  just  as  an 
atom  of  hydrogen  may  pass  from  one  molecule  to  another.  It 
cannot,  however,  be  separated  in  the  free  state  from  any  of  these 
compounds.  It  is  called  ammonium. 


LESSON    XVII. 
AMMONIUM  COMPOUNDS. 

141.  Ammonium  Chloride,  NH4C1. — This  compound  is  formed 
by  the  direct  union  of  ammonia  and  hydrochloric  acid.  During  the 
manufacture  of  illuminating  gas  by  the  distillation  of  coal,  more 
or  less  ammonia  is  formed ;  it  must  be  removed  before  the  gas  is 
fit  for  use,  and  this  is  accomplished  by  washing  the  gas  with  water 
(§  225).  A  dilute  solution  of  ammonia  is  thus  obtained,  and  this 
is  the  source  of  the  ammonia  and  ammo- 
nium compounds  of  commerce.  For  the 
preparation  of  ammonium  chloride  this 
gas  liquor  is  heated  with  lime,  and  the 
ammonia  gas  given  off  is  passed  into 
hydrochloric  acid.  The  solution  is  then 
evaporated,  and  the  residue  of  ammonium 
chloride  is  purified  by  sublimation  in 
stoneware  pots.  It  may  be  formed  by 
another  and  interesting  reaction  :  we  pass 
into  a  jar  of  dry  chlorine  the  drawn-out 
end  of  a  tube  through  which  ammonia  is 
escaping  ;  at  once  the  ammonia  takes  fire, 

being  partially  decomposed  with  production  of  hydrochloric  acid, 

which  at  once  unites  with  another  portion  of  the  ammonia,  forming 

white  clouds  of  ammonium  chloride  (Fig.  55). 

2NH3     -f     3C12     =     N2     +     6HC1 

6HC1     +     6NH3    =     6NH*.C1 


FIG.  55. 


102  t    ct      LESSONS  IN   CHEMISTRY. 

"When  pure,  ammonium  chloride  is  in  translucent  masses, 
which  have  a  fibrous  structure,  and  are  quite  tough  and  difficult 
to  pulverize.  It  dissolves  in  two  and  a  half  times  its  weight  of 
cold  water,  and  in  much  less  hot  water.  Its  taste  is  not  unpleas- 
antly salty  and  sharp.  Unless  in  large  doses,  it  is  not  poisonous. 

142.  Ammonium  Sulphate,  (NH4)2SO,  is  manufactured  by 
passing  into  dilute  sulphuric  acid  the  ammonia  which  is  disen- 
gaged when  gas  liquor  is  heated  with  lime.     It  is  in  white,  color- 
less crystals,  readily  soluble  in  water,  having  a  sharp  taste.     It 
may  be  used  for  the  manufacture  of  ammonia,  and  is  employed  as 
a  fertilizer. 

143.  Ammonium  Sulphydrate,  NH4.SH.  —  We  have  already 
noticed   the   composition   and  mode  of  formation   of  potassium 
sulphydrate  (§  101).     When  hydrogen  sulphide  is  passed  into 
ammonia-water  until  the  liquid  will  dissolve  no  more  of  the  gas, 
ammonium  sulphydrate  is  formed. 

NH3        +        HSH        =        NH4.SH 

It  is  a  colorless  liquid,  but  becomes  yellow  after  it  has  been  for 
some  time  exposed  to  the  air.  Its  odor  is  disgusting,  being  at 
the  same  time  that  of  hydrogen  sulphide  and  that  of  ammonia. 
If  it  be  mixed  with  a  quantity  of  ammonia-water  exactly  equal  to 
that  from  which  it  was  prepared,  ammonium  sulphide  is  formed. 

NR4SH         +         NH3         =         NH^.S.NH*         =         (NH^S 

Ammonium  sulphide. 

This  compound  is  of  much  value  in  the  laboratory  in  detecting 
some  metals.  It  soon  undergoes  partial  decomposition,  and  its 
color  becomes  yellow  from  the  presence  of  dissolved  sulphur. 

To  a  solution  of  ferrous  sulphate  we  add  a  few  drops  of  ammo- 
nium sulphide,  and  a  black  precipitate  of  ferrous  sulphide  is  formed. 

NH4.S.NH*       +  FeSO*          =          (NH«)2S04         +          FeS 

Ammonium  sulphide.      Ferrous  sulphate.        Ammonium  sulphate.      Ferrous  sulphide. 

We  pour  a  few  drops  of  the  same  liquid  into  a  solution  of  zinc 
sulphate,  and  white  zinc  sulphide  is  precipitated. 

(NH*)2S         +         ZnSO*        =  .      (NH4)2SO*         +         ZnS 


144.  On  examining  the  composition  of  the  ammonium  compounds,  we  see 
that  the  radical  NH4  has  the  same  combining  power  as  one  atom  of  hydrogen. 


AMMONIUM    AMALGAM. — NITROGEN    IODIDE.  103 

It  is  a  monatomic  radical ;  but  at  the  same  time  we  notice  that  it  can  replace 
the  hydrogen  atoms  in  the  acids,  and  in  so  doing  it  forms  salts.  It  is  a  basic 
radical,  and  is  in  this  respect  exactly  opposite  to  the  radicals  CIO-  and  SO2, 
which  are  acid  radicals. 

145.  "Ammonium  Amalgam." — We  make  an  amalgam  of 
sodium, — that  is,  a  compound  of  sodium  and  mercury, — by  throw- 
ing on  the  surface  of  a  little  mercury  a  few  small  pieces  of  sodium. 
If  these  do  not  at  once  combine  with  the  mercury,  we  can  readily 
effect  the  combination  by  touching  them  with  a  drop  of  water  on 
the  end  of  a  long  glass  rod.     As  little  pieces  of  burning  sodium 
are  sometimes  thrown  out,  we  keep  the  vessel  at  a  sufficient  dis- 
tance from  the  eyes.     We  now  pour  this  amalgam  into  a  tall  jar 
containing  a  strong  solution  of  ammonium  chloride  :  at  once  a  very 
curious  phenomenon  occurs.     The  mercury  begins  to  swell  and 
become  pasty ;  it  rises  and  floats  on  the  water,  and  sometimes  it 
overflows  the  jar.     On  pouring  it  out  and  examining  it,  we  find 
that  it  has  become  a  brilliant,  butter-like  substance,  and  very 
light.     It  was  formerly  supposed  to  be  free  ammonium  dissolved 
in  mercury — an  amalgam  of  ammonium,  but  is  probably  only 
mercury  inflated  with  hydrogen  and  ammonia.     These  gases 
gradually  escape  and  only  mercury  remains. 

146.  Nitrogen  Iodide. — We  have  reduced  a  small  quantity  of 
iodine  to  a  fine  powder,  and  we  throw  this  into  a  little  ammonia- 
water.     Part  of  it  dissolves,  and  the  other  part  is  converted  into 
a  black  powder,  which  we  carefully  pour  on  a  small  filter  placed 
in  a  funnel.     When  most  of  the  liquid  has  drained  off,  we  dis- 
tribute this  powder  on  several  pieces  of  filter-paper,  which  we  set 
aside  for  the  powder  to  dry.     When  it  is  dry,  the  lightest  touch 
causes  it  to  explode  with  a  loud  noise,  and  sometimes  it  explodes 
spontaneously.     In  any  case  the  explosion  is  always  accompanied 
by  the  production  of  purple  vapors  of  iodine.     The  black  powder 
is  nitrogen  iodide :  there  are  several  such  compounds,  and  their 
composition  depends  on  the  exact  manner  of  formation ;  we  may 
express  it  by  NP.     It  is  formed  by  a  reaction  which  yields  also 
ammonium  iodide. 

4NH3      +     3P      =          3NH4I  +  JJP 

Ammonia.        Iodine.        Ammonium  iodide.        Nitrogen  iodide. 


104  LESSONS    IN    CHEMISTRY. 

The  ammonium  iodide  is  formed  with  a  considerable  produc- 
tion of  energy ;  but  the  liquid  does  not  become  warm,  for  all  this 
energy  is  transferred  to  the  nitrogen  and  iodine  atoms  which  com- 
bine to  form  nitrogen  iodide.  Where  must  we  seek  the  energy  of 
explosion  of  nitrogen  iodide  ?  The  explosion  is  only  a  rearrange- 
ment of  the  atoms ;  a  decomposition  of  the  nitrogen  iodide ;  the 
energy  of  this  decomposition  we  must  consider  as  the  energy  of 
formation  of  nitrogen  molecules  and  iodine  molecules,  of  which  the 
atoms  then  disengage  the  energy  conferred  on  them  by  the  forma- 
tion of  ammonium  iodide,  and  retained  in  the  nitrogen  iodide. 

Nitrogen  chloride,  NCI3,  and  nitrogen  bromide,  NBr3,  have  analogous  com- 
position. They  are  oily  liquids,  and  dangerous  to  prepare.  The  chloride  is 
obtained  by  inverting  a  vessel  filled  with  chlorine  over  warm  solution  of  am- 
monium chloride.  It  collects  in  drops,  which  explode  with  the  utmost  vio- 
lence upon  heating,  in  direct  sunlight,  or  in  contact  with  certain  substances, 
such  as  turpentine  and  phosphorus. 


LESSON    XYIIL 
OXIDES  OP  NITROGEN. 

147.  Nitrous   Oxide,  or  Nitrogen  Monoxide,  N20.— In  a 

glass  flask,  on  a  sand-bath,  we  heat  some  ammonium  nitrate,  a 
white,  crystalline  substance  obtained  by  neutralizing  ammonia 
with  nitric  acid.  Our  flask  being  provided  with  a  delivery-tube, 
we  may  collect  the  gas  over  the  pneumatic  trough  (Fig.  56). 
The  ammonium  nitrate  is  entirely  decomposed  into  water  and 
nitrous  oxide. 

NH*N03  N20  +  2H2Q 

Ammonium  nitrate.  Nitrous  oxide. 

As  the  water  is  converted  into  steam  by  the  heat  required  for  the 
experiment,  when  we  desire  to  collect  the  gas  in  a  gas-bag  we 
pass  it  first  through  an  empty  bottle  in  which  the  steam  may 
condense. 


NITROGEN    MONOXIDE.  105 

148.  Nitrous  oxide  is  a  colorless  gas,  having  no  odor,  but  a 
sweet  taste.  Its  density  is  22  compared  to  hydrogen,  or  1.527 
compared  to  air.  It  is  liquefied  by  great  pressure,  and  con- 
siderable quantities  are  so  liquefied  in  strong  iron  cylinders,  in 


FIG.  56. 

order  that  the  gas  may  be  transported  in  small  bulk  for  the  use 
of  dentists.  At  ordinary  temperatures,  water  dissolves  about  its 
own  volume  of  nitrous  oxide ;  for  this  reason  it  is  advisable  to 
collect  the  gas  over  warm  water. 

Nitrous  oxide  is  decomposed  by  heat,  two  volumes  of  the  gas 
yielding  two  volumes  of  nitrogen  and  one  of  oxygen.  Since  the 
gaseous  mixture  contains  a  much  larger  proportion  of  oxygen 
than  does  the  air,  it  should  support  combustion  better  than  the 
air.  An  experiment  will  show  us  that  it  does ;  we  put  into  a 
jar  of  nitrous  oxide  gas  a  taper  bearing  only  a  spark  of  fire, 
and  this  spark,  decomposing  the  gas  surrounding  it,  sets  fre^ 
sufiicient  oxygen  to  relight  the  taper  (Fig.  57).  In  the  same 
manner  phosphorus  and  sulphur  burn  brilliantly  in  this  gas. 

Nitrous  oxide  is  not  poisonous  ;  it  may  be  inhaled  for  a  short 
time  without  danger,  and  its  inhalation  is  followed  by  insensi- 
bility, a  condition  called  anaesthesia.  Advantage  is  taken  of  this 


106 


LESSONS    IN    CHEMISTRY. 


property  of  the  gas  for  the  performance  of  short  surgical  oper- 
ations. The  first  effects  of  the  inhalation  of  the  gas  are  often  a 
condition  of  excitement  and  disposition  to  gayety  ;  for  this  reason 

it  has  been  called  laughing-gas. 
149.  Nitric  Oxide,  NO.— 
In  a  gas-bottle,  provided  with 
a  delivery-tube  and  funnel; 
tube,  we  have  some  copper  clip- 
pings and  water.  Through  the 
funnel-tube  we  pour  nitric  acid 
until  there  is  a  brisk  disengage- 
ment of  gas.  At  first  this  gas 
in  the  gas-bottle  is  red,  for 
reasons  which  we  shall  presently 
learn,  but  soon  it  becomes  almost 
colorless.  We  then  pass  the  de- 
livery-tube underwater,  and  col- 
lect the  gas  in  jars  filled  with 
water  (Fig.  58).  In  the  reaction 
which  is  taking  place,  the  copper 

is  replacing  the  hydrogen  of  the  nitric  acid,  and  every  atom  of 
copper  replaces  two  atoms  of  hydrogen. 

Cu(N03)2        -|-      2H 
Cupric  nitrate. 

But  in  this  case  the  hydrogen  is  not  set  free ;  it  reduces  more 
nitric  acid,  and  if  we  keep  our  generating  bottle  cool  by  placing 
it  in  cold  water,  the  reduction  yields  NO  and  water.  As  the  cop- 
per atoms  always  set  free  even  numbers  of  hydrogen  atoms,  we 
cannot  write  this  reaction  3H  -f  HNO3  —  2 IPO  +  NO,  but 
must  write  6H  -f  2HN03  =  4H20  +  2NO ;  and  since  the  six 
atoms  of  hydrogen  must  be  replaced  by  three  atoms  of  copper, 
each  of  which  requires  two  molecules  of  nitric  acid  besides  the 
two  that  are  reduced,  we  may  write  the  whole  equation 

3Cu     +     8HN03    =     3Cu(N03)2     +    4H20     +     2NO 
Although  this  gas  contains  but  one  atom  of  oxygen  in  its 


FIG.  57. 


Cu 

Copper. 


2HN03 
Nitric  acid. 


- 


NITRIC   OXIDE. 


107 


•  FIG.  58. 


molecule,  it  was  formerly  called  nitrogen  dioxide:  it  contains 
twice  as  much  oxygen  as  the  monoxide,  or  nitrous  oxide. 

150.  Nitric  oxide  is  a  colorless  gas,  of  which  we  must  remain 
ignorant  of  the  taste 
and  odor,  for  it  forms 
a  corrosive  gas  as  soon 
as  it  is  exposed  to  the 
air.  Its  density  com- 
pared to  air  is  1.039. 
It  is  almost  insoluble 
in  water.  It  has  been 
liquefied  by  great  cold 
and  pressure. 

It  is  decomposed  by  j 
heat,  but  not  so  readily 
as  nitrous  oxide.     For 
this  reason,  although 

it  contains  in  a  given  volume  twice  the  proportion  of  oxygen 
in  nitrous  oxide,  it  will  not  relight  a  taper  bearing  a  spark : 
it  will,  however,  support  the  combustion  of  phosphorus  and 
charcoal. 

The  most  remarkable  property  of  nitric  oxide  is  its  affinity 
for  oxygen.  We  uncover  a  jar  filled  with  the  gas,  and  instantly 
a  cloud  of  red  vapor  is  formed.  This  is  the  red  gas  which  was 
formed  in  the  generating  bottle  when  the  nitric  oxide  first 
eliminated  came  in  contact  with  the  air  in  the  bottle.  In  this 
experiment  each  molecule  of  nitric  oxide  takes  an  atom  of  oxygen 
from  the  air,  and  the  red  vapor  is  the  gas  NO2.  We  must  be 
careful  not  to  inhale  this  gas,  for  it  is  very  injurious. 

We  pour  a  few  drops  of  carbon  disulphide  into  a  jar  of  nitric 
oxide.  The  vapor  of  this  volatile  liquid  at  once  mixes  with  the 
gas,  and  when  we  apply  a  flame,  a  bright  flash  of  light  fills  the 
jar  as  the  carbon  is  burned  by  the  oxygen  of  the  nitric  oxide. 
The  light  produced  by  this  little  explosion  affords  an  excellent 
means  for  causing  the  direct  combination  of  hydrogen  and  chlorine 
(§  71). 


108  LESSONS    IN   CHEMISTRY. 

We  pour  a  little  ferrous  sulphate  solution  into  a  jar  of  nitric 
oxide ;  some  of  the  gas  is  at  once  absorbed,  and  the  liquid  becomes 
brown.  The  nitric  oxide  may  be  driven  out  by  heating  the  solu- 
tion, and  the  pure  gas  is  sometimes  prepared  in  this  manner. 

151.  In  nitric  oxide  the  affinities  of  the  nitrogen  atom  are  not  exhausted  :  we 
have  seen  that  it  is  still  able  to  combine  with  an  atom  of  oxygen.  It  will  also 
combine  with  an  atom  of  chlorine ;  when  one  volume  of  chlorine  is  mixed 
with  two  volumes  of  nitric  oxide,  the  gases  unite,  forming  a  compound  NOC1. 
When  this  compound  is  treated  with  water,  both  substances  are  decomposed, 
yielding  hydrochloric  acid  and  nitrous  acid,  HNO2. 

NOC1     +     IPO         =         HNO2     +     HC1 

Nitric  oxide  may,  then,  act  as  a  radical,  and  in  its  compounds  it  is  called 
nitrosyl.  NOC1  is  therefore  called  nitrosyl  chloride,  and  nitrous  acid  may  be 
called  nitrosyl  hydrate,  NO-OH. 


LESSON    XIX. 
OXIDES    OF  NITROGEN   (Continued). 

152.  Nitrogen  Peroxide,  NO2  and  N204.— We  may  form  this 
substance  by  the  direct  combination  of  nitric  oxide  and  pure  oxy- 
gen, and  we  would  of  course  require  two  volumes  of  the  first  and  one 
volume  of  the  second.  We  can  prepare  it  in  another  manner.  We 

heat  some  dry  lead  nitrate 
in  a  small  retort  placed  in 
a  sand-bath.  The  vapors 
given  off  are  conducted 
into  a  flask  surrounded  by 
ice  (Fig.  59).  Because  the 
lead  nitrate  cannot  well  be 
perfectly  dried,  we  change 
the  receiver  after  a  little 
59  liquid  has  collected  in  it, 

and  throw  away  this  first 

portion.     That  which  now  collects  has  a  yellow  color,  and  if  we 
mix  a  little  salt  with  the  ice  around  the  receiver,  the  liquid  will 


NITROGEN    PEROXIDE.  109 

freeze  to  a  crystalline  mass.     The  lead  nitrate  is  decomposed  into 
lead  oxide,  oxygen,  and  nitrogen  peroxide. 

Pb(N03)2  PbO         +     0     +  N'O* 

Lead  nitrate.  Lead  oxide.  Nitrogen  peroxide. 

The  solid  nitrogen  peroxide  melts  at  — 10°  to  a  nearly  colorless 
liquid ;  this  liquid  becomes  yellow  and  afterwards  orange-colored  as 
the  temperature  rises,  and  at  15°  is  red.  It  boils  at  22°,  giving 
the  red  vapor,  and  the  density  of  this  vapor  compared  to  hydrogen 
is  46,  showing  that  the  molecular  weight  of  the  compound  is  92, 
and  the  molecule  must,  therefore,  contain  N20*.  However,  as  the 
temperature  rises  the  density  diminishes,  and  at  140°  it  is  only 
one-half  46  ;  after  this,  the  density  remains  constant,  the  mole- 
cule has  become  two  molecules,  and  each  of  these  must  contain 
NO2.  Such  decomposition  of  gases  by  heat  is  called  dissocia- 
tion :  we  have  already  noticed  the  dissociation  of  water  vapor 
(§  54)  and  of  nitrous  oxide. 

153.  Nitrogen  peroxide  dissolves  in  water,  but  in  dissolving 
it  reacts  with  the  water ;  with  a  small  quantity  of  water  it  forms 
nitrogen  trioxide  and  nitric  acid,  while  with  a  larger  quantity 
it  yields  nitric  acid  and  nitric  oxide. 

2N20*  +     H20         =         2HN03         +  N203 

Nitrogen  peroxide.  Nitric  acid.  Nitrogen  trioxide. 

3N20*     +     2H20    -    4HN03     +    2NO 
With  the  alkaline  hydroxides  it  yields  nitrates  and  nitrites. 

N20*         +         2NaOH         =         NaNO3         +         NaNO2         +         H20 
Sodium  hydroxide.      Sodium  nitrate.         Sodium  nitrite. 

A  similar  decomposition  really  takes  place  with  water,  but  the 
nitrous  acid  formed  is  at  once  decomposed  by  the  water. 

The  red  vapors  are  dangerous  to  inhale,  and  the  more  dangerous 
because  they  do  not  give  immediate  discomfort.  They  act  on  the 
delicate  membrane  of  the  lungs,  and  there  have  been  many  fata; 
accidents  where  the  gas  has  been  inhaled  by  workmen  repairing 
sulphuric  acid  chambers  (§§  108,  109). 

154.  Nitrogen  Trioxide,  N203. — The  existence  of  this  compound  is  rather 
doubtful.  A  mixture  of  equal  volumes  of  nitric  oxide  and  nitrogen  peroxide, 
upon  cooling  to  a  low  temperature,  condenses  to  a  blue  liquid  which  is  sup- 
posed to  be  N203. 


110  LESSONS    IN    CHEMISTRY. 

The  corresponding  acid  HNO2,  which  would  result  from  the  addition  of  a 
molecule  of  water  to  this  oxide,  has  not  been  isolated. 

N2Q8        +        H20        =        2HN02 

Nitrous  acid. 
The  salts  of  this  acid,  or  nitrites,  are  very  stable. 

155.  Nitrogen  Pentoxide,  N205. — When  dry  chlorine  gas  is  passed  over 
silver  nitrate,  heated  in  a  tube  to  70°,  the  silver  and  chlorine  combine  to- 
gether,   forming   silver   chloride;  oxygen    is   given  off  and  a  volatile   solid 
compound  condenses  in  the  cooler  part  of  the  tube.     This  body  is  nitrogen 
pentoxide,  N205. 

2AgN03    +     Cl2    =    2AgCl    +    N205    +    0 

It  is  more  readily  obtained  from  nitric  acid  by  withdrawing  the  elements  of 
water  by  means  of  phosphorus  pentoxide. 

2HN03      +       P205      =      2HP03      +       N205 

Nitrogen  pentoxide  crystallizes  in  colorless  rhombic  prisms ;  it  melts  at  30° 
and  decomposes  above  45°  with  evolutions  of  brown  fumes.  It  is  liable  to 
explode  spontaneously. 

156.  In   studying  the  other  elements   we  have  examined  the  combining 
powers  of  their  atoms,  compared  to  that  of  an  atom  of  hydrogen, — that  power 
to  which  the  name  atomicity  or  valence  (worth)  has  been  given.     What  is 
the  atomicity  of  the  nitrogen   atom  ?     The  molecule  of  nitrous  oxide  closely 
resembles  in  structure  the  molecule  of  water:  replace  by  two  atoms  of  nitro- 
gen the  two  atoms  of  hydrogen  of  water,  and  we  have  a  molecule  of  nitrous 
oxide.     The  nitrogen    atoms  here  have  the  same   combining   power  as  the 
hydrogen  atoms,  and  we  say  they  are  monatomic.     In  ammonia,  however,  the 
nitrogen  atom  itself  combines  with  three  atoms  of  hydrogen ;  it  must  then  be 
worth  three  hydrogen  atoms,  and  we  call  it  triatomic.     But  in  ammonium 
chloride  it  is  united  with  four  hydrogen  atoms  and  one  chlorine  atom ;  since 
we  have  agreed  that  the  chlorine  atom  has  the  same  worth  as  the  hydrogen 
atom,  the  nitrogen  atom  in  ammonium  chloride  must  be  pentatomic.     Now 
let  us  look  at  the  other  oxygen  compounds  of  nitrogen  :  we  have  seen  that  in 
the  compounds  already  studied  the  oxygen  atom  is  diatomic,  and  indeed  we 
shall  in  time  find  that  there  are  many  reasons  for  believing  that  oxygen  is  al- 
ways diatomic.  Then  in  nitric  oxide,  NO,  the  nitrogen  atom,  which  is  combined 
with  only  one  oxygen  atom,  must  also  be  diatomic;  but  we  have  seen  that  this 
compound  NO  combines  directly  with  a  chlorine  atom,  forming  the  compound 
nitrosyl  chloride,  NO-C1 :  it  combines  with  a  hydroxyl  group,  which  is  mon- 
atomic, forming  nitrous  acid,  HO-NO,  and  in  these  compounds  the  nitrogen 
must  be  triatomic.     We  must  conclude,  however,  that  in  NO2  the  nitrogen  is 
tetratomic,  since  it  is  combined  with  two  atoms  of  diatomic  oxygen,  but  here 
again  a  hydroxyl  group  will  unite  with  the  nitrogen  atom,  which  is  then 
pentatomic  in  nitric  acid,  HNO8.     At  low  temperatures,  when  the  red  vapors 
condense,  forming  molecules  of  N204,  it  seems  also  that  nitrogen  is  penta- 


ATOMICITY   OF    NITROGEN.  Ill 

tomic,  and  that  in  the  molecule  of  N204  two  nitrogen  atoms,  each  of  which 
is  combined  with  two  oxygen  atoms,  are  also  combined  with  each  other. 
If  now  we  remember  our  representations  of  the  combining  powers  of  the 
atoms  by  short  lines,  we  may  see  how  the  atoms  in  these  molecules  seem  to  be 
related,  and  how  the  atomicity  of  nitrogen  varies. 

H 

N-O-N  H-N-H  N=0  C1-N=0 

Nitrous  oxide.         Ammonia.        Nitric  oxide.         Nitrosyl  chloride. 

The  reaction  between  nitrosyl  chloride  and  water  then  becomes  a  double 
decomposition  which  we  can  easily  understand. 

0=N-C1      +      H-O-H     =   0=N-0-H      +      H-Cl 

We  can  understand  also  how  nitrogen  peroxide  decomposes  by  the  action  of 
water,  yielding  nitric  and  nitrous  acids. 

°0±0     +     «-*-=    -    °tH°      + 

Nitrogen  peroxide.        Water.        Nitric  acid.        Nitrous  acid. 

These  formulae,  which  are  called  constitutional  or  graphic  formulae,  do  not 
in  any  manner  represent  the  positions  in  which  the  atoms  are  arranged;  they 
are  intended  to  show  what  atoms  are  in  relations  with  other  atoms  in  the 
molecule.  We  must  believe  that  the  atoms  in  a  molecule  are  in  continual 
motion,  which  we  may  compare  to  the  motions  of  the  planets  around  the  sun, 
and  those  of  the  moons  around  each  particular  planet.  The  nature  of  the 
molecule  depends  on  all  of  its  atoms,  just  as  the  nature  of  a  system  of  planets 
depends  on  the  central  sun  and  all  the  planets  and  their  satellites ;  and  just 
as  the  moon  would  go  with  the  earth  were  that  planet  to  be  withdrawn 
from  the  solar  system,  so  do  certain  groups  of  atoms  enter  into  the  composition 
of  molecules,  from  which  they  may  separate  as  groups  to.  form  part  of  other 
molecules  or  systems  of  atoms. 

Hereafter  we  shall  not  be  obliged  to  use  the  lines  to  represent  the  atomicity 
of  all  the  atoms  in  the  molecules  of  which  we  study  the  structure.  We  know 
that  the  group  hydroxyl,  OH,  is  monatomic,  as  are  also  the  groups  NO  and 
NO3 ;  on  the  other  hand,  we  know  that  the  group  SO2  is  diatomic,  and  we 
can  represent  our  idea  that  each  of  these  groups  exists  in  the  molecule  as  a 
distinct  part  of  the  system  by  separating  it  from  the  rest  of  the  molecule  by  a 
period.  Thus  we  may  represent  nitric  acid  by  the  formula  N02.OH  :  sulphuric 
acid,  by  the  formula  S02.(OH)2. 


112 


LESSONS    IN    CHEMISTRY. 


LESSON    XX. 


NITRIC  ACID.     HNO3. 

157.  Minute  quantities  of  nitric  acid  often  exist  in  the  atmos- 
phere, where  they  are  probably  formed  under  the  influence  of  at- 
mospheric electricity  on  the  nitrogen,  oxygen,  and  moisture  of  the 
air.     Wherever  organized  matters  containing  nitrogen  decompose 
in  the  presence  of  porous  substances  and  alkalies,  such  as  potas- 
sium hydroxide,  sodium  hydroxide,  or  lime,  nitrates  are  formed. 
The  nitric  acid  and  the  nitrates  of  commerce  are  manufactured 
from  nitrates  which  are  found  abundantly  in  some  soils,  par- 
ticularly in  India,  Egypt,  and  Chili :  in  the  latter  country  are 
large  deposits  of  sodium  nitrate. 

158.  We  may  prepare  some  nitric  acid  by  distilling  in  a  glass 


FIG.  60. 


retort  a  mixture  of  sodium  nitrate  and  sulphuric  acid,  and  con- 
densing the  vapor  in  a  flask  surrounded  by  cold  water.  On  the 
large  scale,  the  operation  is  conducted  in  cast-iron  retorts  (Fig. 
60),  and  the  vapor  is  condensed  in  a  series  of  large  stoneware 


NITRIC   ACID.  113 

bottles  which  are  called  bon-bons.  As  in  the  decomposition  of 
sodium  chloride  (§  75),  one  molecule  of  sulphuric  acid  may  be 
made  to  decompose  either  one  or  two  molecules  of  either  potassium 
or  sodium  nitrate,  forming  at  the  same  time  either  a  neutral  or 
an  acid  sulphate,  and  setting  free  one  or  two  molecules  of  nitric 
acid. 

H2SO*     +        NaNO3  NaHSO*  +         HNO3 

Sodium  nitrate.  Sodium  acid  sulphate.  Nitric  acid. 

H2S04     +      2NaN03  Na2SO*  +        2HN03 

The  proportion  required  by  the  last  reaction  is  that  employed 
in  the  arts,  as  it  is  more  economical.  Let  us  see  what  that  pro- 
portion must  be :  the  molecular  weight  of  sulphuric  acid  is 

T  +  3^  +  64*  =  98  J   thafc  °f  Sodium   nitrate  is  ^  ++  u  +  «  =  85' 

Then  98  parts  of  sulphuric  acid,  and  85  of  sodium  nitrate,  if 
perfectly  pure,  would  yield  ^  +  ^  +  ^  =  63  parts  of  nitric  acid. 

Properties. — Nitric  acid  is  a  colorless  liquid,  but  is  partially 
decomposed  by  the  prolonged  action  of  light,  red  vapor  being 
formed  and  communicating  a  yellow  color  to  the  acid  in  which 
it  dissolves.  It  is  very  volatile,  and  its  vapor  condenses  the 
moisture  in  the  air,  producing  white  fumes.  Its  density  is  1.53. 
It  freezes  at  — 49°,  and  boils  at  86°  ;  while  boiling  it  is  par- 
tially decomposed,  so  that  after  a  time  the  boiling  point  rises  to 
120.5°,  and  a  more  dilute  acid  distils,  having  the  same  strength 
as  that  left  in  the  retort.  It  mixes  with  water  in  all  proportions, 
and  the  liquid  becomes  warm  during  the  mixture. 

159.  By  a  red  heat,  nitric  acid  is  at  once  decomposed  into 
water,  red  vapor,  and  oxygen,  a  decomposition  exactly  similar  to 
that  experienced  by  lead  nitrate  under  the  action  of  heat  (§  152). 
2HN03  =  H20  +  2N02  +  0 

In  a  small  crucible,  or  a  thin  iron  dish,  we  heat  some  powdered 
charcoal  until  it  becomes  barely  red  hot.  We  now  remove  it  from 
the  fire,  and,  when  the  dish  has  cooled  a  little,  we  pour,  at  arm's 
length,  some  strong  nitric  acid  on  the  still  hot  charcoal.  At  once 
a  vivid  combustion  takes  place ;  the  oxygen  of  the  decomposed 

8 


114  LESSONS    IN    CHEMISTRY. 

nitric  acid  combines  with  the  carbon,  and  clouds  of  red  vapor  are 
given  off. 

On  the  end  of  a  stick  about  a  metre  long  we  tie  a  test-tube,  into 
which  we  pour  some  strong  nitric  acid,  and  if  our  nitric  acid  is 
not  the  strongest,  we  add  to  it  about  half  its  volume  of  sulphuric 
acid,  which  will  strengthen  the  nitric  acid  by  its  affinity  for  water. 
Then  in  another  iron  dish  we  carefully  warm  some  good  oil  of 
turpentine  until  it  is  nearly  boiling.  Now  we  warm  our  nitric 
acid,  and  standing  at  a  distance,  pour  it  suddenly  into  the  hot 
turpentine :  at  once  the  nitric  acid  oxidizes  the  turpentine,  and, 
unless  the  latter  has  previously  become  thick  by  too  long  exposure 
to  the  air,  it  will  be  inflamed. 

These  experiments  show  us  that  the  oxygen  atoms  have  not 
exhausted  their  energy  in  combining  with  nitrogen.  Indeed,  we 
have  seen  in  the  conversion  of  sulphur  dioxide  into  sulphuric  acid 
that  the  oxygen  of  nitric  acid  is  more  energetic  than-  in  free  oxy- 
gen molecules  at  ordinary  temperatures,  for  we  have  to  heat  oxy- 
gen before  it  will  combine  with  sulphur  dioxide.  By  reason  of 
this  energy  still  existing  in  its  oxygen  atoms,  nitric  acid  is  easily 
reduced ;  that  is,  part  or  all  of  its  oxygen  may  be  readily  removed 
by  oxidizable  bodies.  We  have  seen  how  it  is  reduced  by  the 
hydrogen  of  another,  portion  of  the  acid  when  copper  replaces  that 
hydrogen  (§  149)  :  in  this  same  reaction  part  of  the  nitric  acid  is 
converted  into  nitrous  oxide  and  even  free  nitrogen,  so  that  the 
nitric  oxide  prepared  by  nitric  acid  and  copper  is  never  per- 
fectly pure.  When  the  reduction  by  some  metals  is  carried  out 
to  its  full  limit,  the  nitrogen  combines  with  the  hydrogen,  forming 
ammonia.  This  occurs  in  the  action  of  zinc  on  very  dilute  nitric 
acid:  although  zinc  nitrate  is  then  formed,  no  hydrogen  is  set 
free,  for  the  displaced  hydrogen  reduces  the  nitric  acid  and  com- 
bines with  the  nitrogen :  the  ammonia  formed  at  once  combines 
with  some  of  the  nitric  acid  present,  forming  ammonium  nitrate. 
HNQ3  +  4H2  =  3H2Q  +  NH3 

160.  When  nitric  and  hydrochloric  acids  are  mixed,  a  liquid 
called  nitro-hydrochloric  acid,  or  aqua  regia,  is  obtained.  This 
liquid  is  capable  of  dissolving  gold  and  platinum,  a  power  pos- 


NITRIC    ACID.  115 

sessed  by  neither  of  the  separate  acids.  We  put  a  small  piece 
of  gold-leaf  in  a  test-tube  with  nitric  acid,  and  a  similar  piece 
in  another  tube  with  hydrochloric  acid.  In  neither  tube  is  the 
gold  affected,  but  on  mixing  the  liquids  both  pieces  are  dissolved. 
Nitro-hydrochloric  acid  converts  the  metals  into  chlorides,  the 
hydrogen  of  the  hydrochloric  acid  reducing  the  nitric  acid,  and 
the  chlorine  combining  with  the  metal. 

HNOS    +     3HC1     =    2R2Q     +     NOC1     +     Cl2 

161.  Nitrates. — When  the  hydrogen  of  nitric  acid  is  replaced 
by  metal,  nitrates  are  formed.     We  have  already  learned  that  an 
atom  of  some  metals,  which  we  called  monatomic  metals,  is  capa- 
ble of  replacing  one  atom  of  hydrogen,  while  the  atoms  of  other 
metals  (diatomic)  are  able  to  replace  two.     Since  a  molecule  of 
nitric  acid  contains  only  one  hydrogen  atom,  an  atom  of  zinc  or 
of  lead  must  replace  that  atom  in  two  molecules  of  nitric  acid,  and 
consequently  it  will  be  united  to  two  groups,  NO3.     Then,  while 
we  can  express  the  molecules  of  potassium  and  sodium  nitrates  by 
the  formulae  KNO3  and  NaNO3,  we  must  write  the  molecules  of 
lead  and  zinc  nitrates  Pb(N03)2  and  Zn(N03)2. 

162.  Into  a  test-tube  containing  some  solution  of  potassium 
nitrate  in  water,  we  pour  a  little  solution  of  ferrous  sulphate,  and 
then,  inclining  the  tube,  some  strong  sulphuric  acid.     This  last, 
being  much  heavier  than  the  other  liquids,  does  not  mix  at  once 
with   the  solution,  but  at  the  surface,  where  the  sulphuric  acid 
below  and  the  solution  of  the  nitrate  touch,  a  dark  ring  is  formed. 
This  is  caused  by  a  partial  reduction  of  the  nitric  acid  by  the  fer- 
rous sulphate,  which  produces  at  the  same  time  a  dark  color  with 
the  nitric  oxide  resulting  from  the  reduction.     This  color  disap- 
pears if  we  heat  the  tube  (§  150).    This  is  our  test  for  nitric  acid 
and  nitrates. 


116  LESSONS    IN    CHEMISTRY. 

LESSON    XXI. 
NITRATES. 

163.  All  of  the  nitrates  are  soluble  in  water.     Some  of  them 
form  anhydrous  crystals ;  others  require  water  of  crystallization. 
When  thrown  on  hot  coals,  they  decompose,  and  the  oxygen  given 
off  increases  the  intensity  of  the  combustion.     Salts  which  so  pro- 
mote combustion  are  said  to  deflagrate  on  hot  coals. 

164.  Sodium  Nitrate,  NaNO3,  is  found  in  large  quantities  in 
Chili  and  Peru.     It  forms  rhombohedral  crystals  that  are  almost 
cubical ;  it  is  very  soluble  in  water.     It  attracts  moisture  from 
the  air,  and  this  property  prevents  its  use  in  the  manufacture  of 
gunpowder  (see  §  166).     It  is  from  sodium  nitrate  that  nitric 
acid  and,  indirectly,  most  of  the  other  nitrates  are  prepared. 

1 65.  Potassium  Nitrate,  KNO3. — This  salt  is  commonly  called 
nitre  or  saltpetre.    In  some  hot  countries  it  forms  an  efflorescence, 
or  white  powder,  on  the  surface  of  the  soil,  and  may  be  obtained 
by  washing  the  soil  with  water  and  evaporating  the  resulting  solu- 
tion.    It  is  generally  made  by  a  double  decomposition  between 
sodium    nitrate,    or    Chile   saltpetre,    and    potassium    chloride. 
When  boiling  solutions  of  the  two  substances  are  mixed,  the 
sodium  chloride  crystallizes  out.     It  is  removed  by  passing  the 
hot  solution  through  a  canvas  filter;  upon  cooling,  the  potassium 
nitrate  separates  from  the  filtrate. 

KCl  +  NaNO3        =  NaCl         -f  KNO3 

Potassium  chloride.  Sodium  nitrate.  Sodium  chloride.  Potassium  nitrate. 

Potassium  nitrate  forms  long,  six-sided  prisms  which  have  a 
bitter  and  cooling  taste.  They  dissolve  in  about  five  times  their 
weight  of  water  at  ordinary  temperatures,  but  require  less  than 
half  their  weight  of  boiling  water.  We  can  now  understand  how 
this  compound  may  be  separated  from  sodium  chloride,  which  is 


GUNPOWDER.  117 

about  equally  soluble  in  hot  and  cold  water ;  for  when  a  boiling  satu- 
rated solution  of  potassium  nitrate  is  cooled  to  ordinary  tempera- 
tures, nine-tenths  of  the  salt  separate  in  crystals,  but  from  a  boiling 
saturated  solution  of  common  salt  very  little  is  deposited  on  cooling. 

Potassium  nitrate  deflagrates — that  is,  increases  the  activity  of 
combustion — when  thrown  on  hot  coals.  We  melt  some  zinc  in 
an  iron  ladle,  and,  when  it  is  nearly  red  hot,  we  throw  in  a  few 
small  pieces  of  potassium  nitrate :  the  metal  takes  fire  aod  burns 
into  zinc  oxide,  the  oxygen  being  supplied  from  the  decomposing 
potassium  nitrate. 

166.  Gunpowder  is  a  mixture  of  about  seventy-five  parts  of  potas- 
sium nitrate,  ten  of  sulphur,  and  fifteen  of  charcoal.  It  is  made 
by  grinding  each  substance  separately  to  the  finest  powder,  and 
then  mixing  them  and  grinding,  after  a  little  water  has  been  added. 
The  intimate  mixture  is  then  strongly  pressed  and  carefully  dried 
in  a  warm  room,  after  which  it  is  broken  into  grains  and  these  are 
sifted  into  various  sizes.  The  grains  are  polished  by  friction  over 
each  other  in  rotating  barrels.  This  mixture  contains  all  of  the 
materials  necessary  for  its  own  combustion,  and  the  result  of  the 
explosion  may  be  generally  expressed  by  saying  that  the  sulphur 
combines  with  the  potassium,  forming  potassium  sulphide,  while 
the  oxygen  of  the  nitre  unites  with  the  carbon  to  form  the  gases 
carbon  monoxide  and  carbon  dioxide,  which,  together  with  the 
nitrogen,  are  set  free.  The  gas  occupies  a  volume  very  much 
greater  than  that  of  the  powder  which  produced  it,  and  this  large 
volume  is  made  still  larger  by  the  high  temperature  of  the  reaction. 
Of  course  the  outside  of  the  grains  of  powder  must  burn  first,  and 
the  larger  the  grains  the  slower  the  combustion  and  the  consequent 
production  of  gas ;  but  the  smaller  the  grains  the  more  rapidly  is 
each  burned  and  the  flame  carried  from  one  to  the  other.  Hence 
the  small  quantity  of  powder  used  in  small-arms  is  in  fine  grains 
in  order  to  produce  instantly  as  much  force  as  possible ;  but  large 
guns  would  be  broken  by  such  sudden  strain,  and  large  grains  or 
lumps  are  employed,  which  are  put  into  the  gun  in  coarse  bags. 
In  blasting,  if  it  is  desired  to  break  the  rock  in  small  pieces,  a  very 
quickly  burning  powder  is  used ;  but  if  it  is  desired  to  split  off 


118  LESSONS    IN    CHEMISTRY. 

large  masses,  the  effect  is  accomplished  by  the  more  slowly  in- 
creasing pressure  from  a  slower  powder. 

167.  Silver  Nitrate,  AgNO3,  is  made  by  dissolving  silver  in 
nitric  acid,  and  evaporating  the  solution  until  it  crystallizes.     It 
forms  colorless  plates,  soluble  in  their  own  weight  of  water.     Its 
color  darkens  by  the  action  of  the  organic  matter  in  the  air  and 
exposure  to  light.    It  melts  when  cautiously  heated,  and  when  cast 
into  sticks  forms  the  lunar  caustic  used  by  surgeons.     It  is  a  cor- 
rosive body,  and  in  the  presence  of  moisture  destroys  the  tissues. 
Should  any  of  it  by  accident  be  swallowed,  common  salt  is  its  anti- 
dote ;  insoluble  silver  chloride  is  then  formed,  and  this  is  com- 
paratively harmless  (§  75).     When  silver  nitrate  is  highly  heated, 
it  leaves  a  residue  of  pure  silver. 

168.  Strontium   Nitrate,  Sr(N03)2.— This  salt  is  made  by 
dissolving  the  mineral  strontianite,  which  is  strontium  carbonate, 
in  nitric  acid,  and  purifying  by  several  crystallizations.     It  forms 
colorless  crystals,  quite  soluble  in  water. 

169.  Barium  Nitrate,  Ba(N03)2,  is  obtained  like  the  preceding 
salt,  but  witherite — barium  carbonate — is  used.    It  also  forms  color- 
less crystals,  soluble  in  water,  and  the  solution  may  be  used  as  a  test 
for  sulphuric  acid  (§  115). 

170.  Cupric  Nitrate,  Cu(N03)2  -J-  3H20,  remains  in  the  bottle 
in  which  we  prepare  nitric  oxide.     If  we  filter  and  evaporate  this 
solution,  the  salt  separates  in  large  blue  prisms ;  it  is  very  corrosive. 
When  strongly  heated,  it  leaves  black,  cupric  oxide. 

171.  Mercuric  Nitrate,  2Hg(N03)2+H20,  separates  in  large, 
colorless  crystals  when  we  cool  in  ice  and  salt  the  solution  obtained 
by  boiling  mercury  in  a  large  quantity  of  nitric  acid.     Its  solution 
is  an  energetic  caustic,  and  is  used  in  surgery.     When  dry  mer- 
curic nitrate  is  heated,  it  decomposes  just  as  the  nitrates  of  lead 
and  copper,  leaving  red  mercuric  oxide. 

Hg(N03)2    =     HgO     +     2N02     +     0 

172.  Lead  Nitrate,  Pb(N03)2.— This  compound,  which  is  one 
of  our  most  soluble  lead  salts,  is  made  by  boiling  lead  oxide  (lith- 
arge) in  nitric  acid,  and  evaporating  the  solution  until  crystals 
separate. 


PHOSPHORUS. 


119 


PbO     +     2HN03     =     Pb(N03)2     +     H20 

It  forms  colorless,  anhydrous  crystals,  very  soluble  in  boiling  water, 
and  in  seven  times  their  weight  of  cold  water. 


LESSON    XXII. 
PHOSPHORUS.— HYDROGEN   PHOSPHIDE. 

173.  Phosphorus,  P=31. — The  element  phosphorus  is  extracted 
from  bones,  in  which  it  exists  in  a  compound  known  as  calcium 


phosphate.  The  bones  are  first  burned,  to  remove  all  of  the  ani- 
mal matters,  and,  by  a  process  which  we  will  understand  better 
when  we  study  the  acids  of  phosphorus,  the  calcium  phosphate 
which  remains  is  converted  into  calcium  metaphosphate.  This 
last  body  is  mixed  with  charcoal  and  strongly  heated  in  clay  retorts, 
and  the  phosphorus  vapor  is  condensed  in  vessels  containing  cold 
water  (Fig.  61).  In  the  reaction  which  takes  place,  only  half  of 
the  phosphorus  is  separated  from  the  bone-ash,  and  there  is  left  in 
the  retorts  a  compound  called  calcium  pyrophosphate,  while  the 
gas  carbon  monoxide  is  disengaged. 


120  LESSONS    IN   CHEMISTRY. 

4Ca(P03)2  +  IOC      =          2Ca2P2Q7  +          10CO  +  P* 

Calcium  metaphosphate.      Carbon.      Calcium  pyrophosphate.      Carbon  monoxide. 

A  simpler  process  has  been  recently  introduced.  It  consists  in  heating  a 
mixture  of  bone-ash,  charcoal,  and  a  flux  by  means  of  a  powerful  electrical 
current :  phosphorus  distils  over,  while  the  residue  forms  a  liquid  slag. 

Small  particles  of  charcoal  are  carried  over  with  the  phos- 
phorus, which  is  purified  by  enclosing  it  in  chamois-skin  bags  and 
melting  it  under  warm  water.  The  melted  phosphorus  is  then 
squeezed  through  the  leather,  and  so  purified  is  drawn  up  into 
glass  tubes,  where  it  is  allowed  to  harden  in  the  form  of  sticks.  It 
is  always  kept  under  water,  and  is  transported  in  sealed  tin  cans. 

174.  PROPERTIES. — Phosphorus  is  an  almost  colorless,  wax- 
like  solid.     It  is  flexible,  and  soft  enough  to  be  readily  scratched 
by  the  finger-nail.     When  it  has  been  exposed  to  light  for  a  long 
time,  its  surface  becomes  white  and  opaque ;  it  is  covered  with 
little  crystals  of  phosphorus ;  these  become  loosened,  and  if  we 
shake  the  bottle  in  the  dark  the  whole  of  the  liquid  is  luminous. 
Phosphorus  has  a  peculiar,  somewhat  garlicky  odor.     Its  density 
is  1.83.     It  melts  at  44°,  and   boils  at  290°.     Its  density  com- 
pared to  hydrogen  is  62 ;  the  densities  of  its  gaseous  compounds, 
and  the  composition  of  all  its  compounds,  show  that  its  atomic 
weight  is  31 ;  therefore  the  molecule  of  phosphorus  vapor  must 
contain  four  atoms,  if  the  molecule  of  hydrogen  contains  two. 
That  is,  two  volumes  of  hydrogen  weighing  2  represent  two  atoms, 
but  two  volumes  of  phosphorus  vapor  weighing  124  contain  four 
atoms.     A  number  of  other  elements  also  have  molecules  contain- 
ing four  atoms.     Phosphorus  is  insoluble  in  water,  but  dissolves 
slightly  in  most  oils :  it  dissolves  freely  in  carbon  disulphide,  and 
separates  in  small  crystals  when  the  solution  is  evaporated  very 
slowly.    Phosphorus  is  luminous  in  the  dark,  and  this  phenomenon 
is  probably  caused  by  a  slow  oxidation. 

175.  Phosphorus  has  an  energetic  affinity  for  oxygen.     If  we 
expose  to  the  air  a  small  piece  of  dry  phosphorus  on  a  plate,  after 
a  time  the  heat  developed  by  the  slow  combustion  is  sufficient  to 
ignite  the  phosphorus,  which  takes  fire  at  a  temperature  of  50°. 
If  we  pour  on  a  piece  of  dry  paper  on  a  plate  a  few  cubic  centi- 


RED   PHOSPHORUS.  121 

metres  of  a  solution  of  phosphorus  in  carbon  disulphide,  the  latter 
evaporates,  leaving  the  phosphorus  in  a  state  of  fine  division. 
These  small  particles  are  surrounded  by  oxygen,  and  the  tem- 
perature quickly  rises  till  they  burst  into  flame. 

Phosphorus  is  very  poisonous  :  even  when  poisoning  by  it  is  not 
rapidly  followed  by  death,  dangerous  diseases  of  the  liver,  heart, 
kidneys,  and  tongue  are  produced,  and  these  are  usually  fatal. 

176.  Red  Phosphorus. — The  properties  which  have  just  been 
described  are  those  of  the  common  form  of  phosphorus,  but  there 
is  another  form  which  may  be  obtained  by  heating  ordinary  phos- 
phorus for  a  long  time  to  240°.     It  then  becomes  a  brownish-red 
and  opaque  mass.     This  modification  of  phosphorus  has  no  odor 
or  taste,   and  is  not  poisonous.     It  is  not  luminous  in  the  dark, 
and  does  not  melt  nor  take  fire  below  240° ;  it  is  not  soluble  in 
carbon  disulphide.     We  may  easily  make  a  little  of  this  red  phos- 
phorus.    We  put  a  piece  of  dry  phosphorus  in  a  test-tube,  and 
drop  on  it  a  very  small  flake  of  iodine ;  the  iodine  combines  vio- 
lently with  part  of  the  phosphorus,  producing  light  and  heat ;  but 
the  remainder  of  the  phosphorus  is  converted  into  a  hard  black 
mass.    When  we  break  the  tube,  and  powder  the  residue,  we  find 
it  has  a  chocolate  color :  it  is  red  phosphorus. 

While  red  phosphorus  does  not  take  fire  as  readily  as  ordi- 
nary phosphorus,  its  chemical  properties  are  unchanged.  We 
mix  a  small  quantity  of  moist  amorphous  phosphorus  with  pow- 
dered potassium  chlorate,  and  distribute  the  mixture  on  several 
pieces  of  paper  which  we  set  aside  to  dry.  When  quite  dry,  the 
least  pressure  on  the  spot  containing  the  mixture  will  cause  the 
oxidation  of  the  phosphorus  and  decomposition  of  the  potassium 
chlorate  with  a  loud  explosion. 

When  red  phosphorus  is  heated  to  260°  it  changes  into  ordi- 
nary phosphorus. 

177.  Large  quantities  of  phosphorus  are    employed   for   the 
manufacture  of  matches.     The  flame  of  phosphorus  alone  would 
not  ignite  the  stick,  because  this  would  become  coated  with  the 
phosphoric  oxide  formed,  and  the  latter  is  a  bad  conductor  of 
heat.    Common  matches  are  therefore  first  tipped  with  paraffin  or 


122  LESSONS   IN    CHEMISTRY. 

sulphur,  which  may  take  fire  from  the  phosphorus,  and  the  ends 
of  the  sticks  are  then  dipped  in  a  paste  of  ordinary  phosphorus 
with  strong  glue  and  some  coloring  matter.  The  brown-headed 
or  parlor  matches  are  tipped  with  a  paste  made  of  red  phos- 
phorus and  potassium  chlorate,  and  sometimes  antimony  sul- 
phide. The  heads  of  the  safety  matches,  which  light  only  on  the 
box,  contain  potassium  chlorate  and  antimony  sulphide,  and 
these  are  ignited  by  friction  with  red  phosphorus  glued  to  the 
side  of  the  box. 

Burns  by  phosphorus  are  quite  painful  and  difficult  to  heal. 
They  are  really  poisoned  wounds,  for  part  of  the  metaphosphoric 
acid  (§  187),  formed  by  the  action  of  the  phosphoric  oxide  on 
the  skin,  is  absorbed,  and  the  gravity  of  the  burn  is  much  greater 
than  that  of  an  ordinary  burn  of  the  same  size.  Phosphorus 
should  always  be  cut  under  water,  and  removed  from  the  water 
and  dried  between  folds  of  filter-paper  only  at  the  instant  before 
using. 

178.  Hydrogen  Phosphide,  PH3. — In  a  small  glass  retort 
which  we  have  completely  filled  with  a  rather  strong  solution  of 

•sodium  hydrate,  we  put  some 
small  pieces  of  phosphorus, 
and  after  arranging  the  beak 
of  the  retort  under  the  sur- 
face of  water  contained  in  a 
small  vessel,  we  apply  a  gentle 
heat  (Fig.  62).  When  the 
liquid  begins  to  boil,  bubbles 

_,        2  of  gas  rise  through  the  water, 

and  as   each  bubble   comes 

into  the  air  it  takes  fire  and  produces  a  ring  of  white  smoke. 
When  the  air  is  perfectly  still,  we  notice  the  curious  motions  of  the 
rings.  The  gas  which  is  being  formed  is  hydrogen  phosphide, 
having  the  composition  PH3,  and  as  it  burns  the  hydrogen  is 
converted  into  water,  and  the  phosphorus  into  phosphoric  oxide 
which  forms  the  wreaths  of  smoke.  Hydrogen  phosphide  is  not, 
however,  the  only  product  of  the  reaction.  Part  of  the  phos- 


OXIDES    AND   ACIDS   OP   PHOSPHORUS.  123 

phorus  has  been  oxidized  at  the  expense  of  some  decomposed 
water,  and  the  sodium  has  entered  into  the  new  molecule.  As  we 
know  by  analysis  that  only  sodium  hypophosphite,  having  the 
composition  NaH2P02,  and  hydrogen  phosphide  are  formed,  we 
may  write  the  rather  difficult  reaction, 

SNaOH         +      P*     +     3H2Q      =         3NaH2P02  +  PH^ 

Sodium  hydroxide.  Sodium  hypophosphite. 

The  molecule  of  hydrogen  phosphide  has  a  composition  like 
that  of  ammonia,  NH3.  Indeed,  it  will  under  proper  conditions 
combine  directly  with  acids,  like  ammonia,  and  its  compounds, 
which  then  contain  the  group  PH4,  are  called  phosphonium  salts. 
PH4I,  phosphonium  iodide,  is  the  most  stable  of  these. 

If  we  heat  red  hot  in  an  earthen  crucible  some  fragments  of  quick-lime,  and, 
having  a  cover  for  one  crucible,  throw  in  some  pieces  of  phosphorus,  covering 
the  crucible  after  introducing  each  piece,  a  calcium  phosphide  is  formed  in 
the  crucible.  When  the  crucible  and  contents  have  cooled,  we  may  throw  some 
of  the  pieces  of  the  calcium  phosphide  into  water ;  bubbles  of  hydrogen  phos- 
phide then  come  to  the  surface  and  take  fire  spontaneously,  forming  wreaths  of 
smoke  as  before.  Pure  hydrogen  phosphide  does  not  take  fire  on  coming  into 
the  air,  unless  the  water  through  which  it  passes  is  boiling.  That  which  we 
have  just  prepared  contains  a  trace  of  another  compound  of  phosphorus  and 
hydrogen  which  is  spontaneously  inflammable. 

179.  Phosphorus  Chlorides.— There  are  two  chlorides  of  phosphorus. 
Phosphorus  trichloride,  PCI3,  is  a  volatile,  colorless  liquid.  It  is  made  by  pass- 
ing chlorine  over  phosphorus  and  condensing  the  vapor  which  distils.  Phos- 
phorus pentachloride,  PCI5,  is  a  pale  yellow,  crystalline  solid.  It  is  obtained 
by  passing  chlorine  into  the  trichloride  until  the  whole  becomes  solid.  Both 
of  these  bodies  are  decomposed  by  water,  as  we  shall  presently  see. 


LESSON    XXIII. 
OXIDES   AND  ACIDS   OF  PHOSPHORUS. 

180.  There  are  two  oxides  of  phosphorus,  a  trioxide,  P*06,  and 
a  pentoxide,  P205.  The  trioxide  is  formed  when  phosphorus  is 
slowly  oxidized  in  dry  air.  The  pentoxide,  often  called  phosphoric 
oxide,  results  when  phosphorus  is  burned  in  a  full  supply  of  air 


124  LESSONS   IN   CHEMISTRY. 

or  oxygen.  We  place  a  piece  of  phosphorus  ia  a  small  dish  on 
a  plate,  and,  after  igniting  it,  cover  the  dish  with  a  bell-jar.  In  a 
short  time  the  phosphoric  oxide  formed  settles  on  the  dish  and 
sides  of  the  jar  in  the  form  of  a  snowy-white  powder.  When  we 
sprinkle  some  drops  of  water  on  this  powder,  a  hissing  noise  is 
heard ;  the  water  and  phosphoric  oxide  combine,  producing  much 
heat  and  an  acid  of  phosphorus.  The  composition  of  the  acid 
which  is  thus  formed  depends  on  the  temperature  of  the  water, 
for  one  molecule  of  this  same  phosphoric  oxide  is  able  to  react 
with  one,  two,  or  three  molecules  of  water,  forming  three  different 

acids. 

P2Q5  +  H20  -  2IIP03,  Metaphosphoric  acid. 

P205  +  2H20  =  H4P207,  Pyrophosphoric  acid. 

P205  +  3H20  =  2H3P04,  Orthophosphoric  acid. 

We  shall  presently  study  these  acids.  Besides  these  there  are 
two  others.  Of  one  we  have  seen  the  formation  of  a  salt,  sodium 
hypophosphite ;  the  corresponding  acid  is  of  course  hypophos- 
phorous  acid,  H3P02.  The  other  is  formed  by  the  reaction  of 
phosphorus  trioxide  on  water,  and  one  molecule  of  the  trioxide 
reacts  with  six  molecules  of  water,  forming  four  molecules  of 
phosphorous  acid. 

We  then  have  a  series  of  acids. 

H3P02,  Hypophosphorous  acid. 

H3P03,  Phosphorous  acid. 

H3P04,  Orthophosphoric  acid. 

H4P207,  Pyrophosphoric  acid. 

HPO3,  Metaphosphoric  acid. 

181.  Hypophosphorous  Acid  may  be  made  by  boiling  phos- 
phorus with  barium  hydroxide,  Ba(OH)2,  and  by  the  cautious  ad- 
dition of  sulphuric  acid  exactly  precipitating  the  barium  from  the 
barium  hypophosphite  formed.  After  filtering,  the  liquid  is  con- 
centrated until  a  thick  syrup  is  obtained.  This  is  hypophosphorous 
acid.  Although  a  molecule  of  this  acid  contains  three  atoms  of 
hydrogen,  only  one  of  those  atoms  is  replaceable  by  metal.  It  is 
a  monobasic  acid,  and  its  salts  with  a  monatomic  metal  like  sodium 
will  contain  one  atom  of  metal  and  the  group  H2P02.  The  hypo- 
phosphites  of  diatomic  metals  must  contain  two  of  these  groups 


ORTHOPHOSPHORIC   ACID.  125 

in  order  that  two  atoms  of  hydrogen  may  be  replaced :  barium 
hypophosphite  will,  then,  be  Ba(H2P02)2. 

182.  Phosphorous  Acid  is  most  quickly  prepared  by  the  re- 
action of  phosphorus  trichloride  with  water,  one  molecule  of  the 
trichloride  requiring  three  molecules  of  water. 

PCI3     +     3H2Q    =     H3P03     +     3HC1 

It  is  a  dibasic  acid :  it  contains  two  atoms  of  replaceable  hydro- 
gen; we  may  have  a  sodium  phosphite,  Na2HP03,  and  a  sodium 
acid  phosphite,  NaH2P03.  Barium  phosphite  would  be  BaHPO3. 
Both  hypophosphorous  and  phosphorous  acids  have  reducing 
properties;  that  is,  they  will  take  away  oxygen  from  oxidized 
bodies,  so  becoming  converted  into  phosphoric  acid.  Into  a  test- 
tube  containing  a  solution  of  silver  nitrate,  we  pour  some  solution 
of  sodium  hypophosphite  :  in  a  short  time  the  interior  of  the  tube 
is  coated  with  metallic  silver  by  the  reducing  action  of  the  hypo- 
phosphite. 

183.  Orthophosphoric  Acid. — We  have  seen  how  this  acid, 
which  is  commonly  called  phosphoric  add,  may  result  from  the 
action  of  water  on  phosphoric  oxide.     It  is  also  formed  by  the 
reaction  of  phosphorus  pentachloride  with  water. 

PCI*     +     4H20     =     H3PO*     +     5HC1 

It  is  usually  made  by  boiling  amorphous  phosphorus  with  nitric 
acid,  which  is  reduced,  red  vapors  being  given  off.  The  liquid  is 
then  evaporated  to  a  small  bulk,  and  put  in  a  bell-jar  over  a  dish 
containing  sulphuric  acid,  which  gradually  absorbs  the  remain- 
ing moisture.  In  this  manner  hard,  transparent,  and  deliquescent 
crystals  of  orthophosphoric  acid  are  obtained. 

Orthophosphoric  acid  is  tribasic :  its  molecule  contains  three 
atoms  of  replaceable  hydrogen.  Consequently  it  may  with  the 
same  metal  form  three  different  salts,  accordingly  as  one,  two,  or 
three  atoms  of  hydrogen  are  replaced  by  a  corresponding  quantity 
of  the  metal.  The  names  of  these  salts  should  indicate  the  number 
of  hydrogen  atoms  which  have  been  replaced,  or  the  number  of 
metallic  atoms  which  have  replaced  the  hydrogen  :  thus,  since  one 
atom  of  sodium  always  replaces  one  of  hydrogen,  monosodbim 
phosphate  is  NaH2PO*,  disodium  phosphate  is  Na2HP04,  and  tri- 


126  LESSONS    IN    CHEMISTRY. 

sodium  phosphate  is  Na3P04.  We  have  already  learned  by  several 
reactions  (§§  118,  136)  that  one  atom  of  calcium  is  capable  of  re- 
placing two  atoms  of  hydrogen  ;  and  if  we  perfectly  neutralize 
orthophosphoric  acid  with  lime  (calcium  oxide),  we  must  have 
two  molecules  of  the  acid  and  three  of  lime. 

2H3PO*  +  3CaO  =  Ca3(PO*)2  +  3H20 
The  tricalcium  phosphate  so  formed  is  the  compound  existing 
in  bone-ash,  from  which  phosphorus  is  obtained.  It  is  insoluble 
in  water ;  when  it  is  treated  with  sulphuric  acid,  two  atoms  of 
calcium  are  taken  from  its  molecule,  forming  calcium  sulphate, 
while  calcium  acid  phosphate  passes  into  the  solution. 

Ca3(P04)2       +      2R2SO*       =        CaH*PO*  +        2CaSO* 

Tricalcium  phosphate.  Calcium  acid  phosphate.      Calcium  sulphate. 

The  calcium  sulphate,  being  insoluble,  is  separated  by  nitration, 
and  the  calcium  acid  phosphate  is  converted  into  calcium  meta- 
phosphate  by  the  action  of  heat,  which  decomposes  it  with  the 
formation  of  water. 

CaH4(PO*)3  Ca(P03)2  +    2H20 

Calcium  acid  phosphate.        Calcium  metaphosphate. 

184.  To  a  solution  of  disodium  phosphate — either  of  the  other 
orthophosphates  would  answer — we  add  a  little  ammonia-water, 
and  then  some  magnesium  sulphate  solution.    A  white  precipitate 
forms ;  this  contains  both  ammonium  and  magnesium  ;  two  atoms 
of  hydrogen  in  phosphoric  acid  are  here  replaced  by  one  atom  of 
magnesium,  and  the  other  by  the  ammonium  group,  NH*. 

Na2HPO*    +     MgSO4     +  NH3  =   Na2S04      +      Mg(NH4)P04 
Disodium  Magnesium  Sodium  Ammonio- 

phosphate.  sulphate.  sulphate.       magnesium  phosphate. 

In  another  test-tube  we  mix  some  solutions  of  disodium  phos- 
phate and  silver  nitrate.  A  yellow  precipitate  of  trisilver  phos- 
phate forms. 

Na2HPO*     +     3AgN03    =     Ag3PO*     +     2NaN03     +     HNO3 

These  reactions  enable  us  to  identify  orthophosphoric  acid  and 
the  orthophosphates. 

185.  ORTHOPHOSPHATES. — Disodium  phosphate  exists  in  the 
blood,  and  the  phosphorus  which  is  eliminated  from  our  bodies  is 


PYROPHOSPHORIC   ACID.     •  127 

principally  in  monosodium  phosphate,  which  passes  out  in  the 
urine.  The  phosphates  containing  only  one  atom  of  metal  redden 
blue  litmus,  and  are  generally  called  acid  phosphates.  Those 
containing  two  atoms  of  metal  do  not  affect  litmus,  and  are  gen- 
erally called  neutral  or  common  phosphates ;  while  those  having 
three  atoms  of  metal  turn  red  litmus  to  blue. 

Large  mineral  deposits  of  tricalcium  phosphate  exist  in  many 
localities,  and  it  is  probable  that  they  have  been  formed  from  ac- 
cumulations of  bones  during  prehistoric  ages.  The  mineral  apa- 
tite, generally  green  in  color,  is  principally  tricalcium  phosphate. 

186.  Pyrophosphoric  Acid. — When  orthophosphoric  acid  is 
long  heated  to  a  temperature  of  about  213°,  it  undergoes  partial 
decomposition  :  two  molecules  lose  one  molecule  of  water,  and  then 
combine  together,  forming  a  molecule  of  pyrophosphoric  acid. 

2R3PO*    =     H2Q     +     H4P2QT 

We  can  understand  this  better  if  we  consider  the  structure  of  the  molecule 
of  phosphoric  acid:  it  must  contain  three  hydroxyl  groups,  and  the  other 
atom  of  oxygen  must  be  combined  directly  with  the  phosphorus  atom.  By  the 
removal  of  the  elements  of  one  molecule  of  water,  two  groups,  each  containing 
one  phosphorus  atom,  one  oxygen  atom,  and  two  hydroxyl  groups,  will  be 
cemented,  we  may  say,  by  an  atom  of  oxygen. 

OH       OH          OH  OH 
HO-PrO  +  HO-P^O     =   0=P-0-PrO    +  HOH 
OH       OH  OH  OH 

Two  molecules  orthophosphoric  acid.        Pyrophosphoric  acid. 

We  see  then  that  in  certain  compounds,  such  as  hydrogen  phosphide  and 
phosphorus  trichloride,  phosphorus  is  triatomic,  but  that  in  other  cases,  and 
these  are  the  most  numerous,  it  is  pentatomic,  or  equivalent  to  five  atoms  of 
hydrogen. 

We  mix  some  solutions  of  sodium  pyrophosphate  and  silver 
nitrate;  instantly  a  white  precipitate  of  insoluble -silver  pyrophos- 
phate is  formed. 

Na*PW     +     4AgNO»     =     AgfP'O*     +     4NaN03 

187.  Metaphosphoric   Acid. — When  either  orthophosphoric 
or  pyrophosphoric  acid  is  heated  to  redness,  water  is  formed,  and 
there  remains  a  hard,  glass-like  mass  of  metaphosphoric  acid. 

H'PO*    =     HPO3    +    H20 


128  LESSONS    IN    CHEMISTRY. 

If  an  acid  phosphate  is  heated  in  the  same  manner,  it  undergoes 
a  similar  decomposition,  and  a  metaphosphate  remains  (§  183). 

Metaphosphoric  acid  quickly  coagulates  or  renders  insoluble  the 
albumen  of  white  of  egg,  a  property  which  distinguishes  it  from 
both  ortho-  and  pyrophosphoric  acids. 

Metaphosphoric  and  pyrophosphoric  acids  and  their  salts  are 
poisonous,  as  are  also  hypophosphorous  and  phosphorous  acids,  but 
orthophosphoric  acid  and  the  orthophosphates  are  not  poisonous 
unless  in  such  concentrated  form  as  to  be  corrosive. 

188.  When  either  metaphosphoric  or  pyrophosphoric  acid,  or 
any  of  their  salts,  is  boiled  with  nitric  acid,  orthophosphoric  acid  or 
one  of  its  salts  is  formed.  We  have  already  seen  that  phosphorus 
itself  is  oxidized  to  orthophosphoric  acid  by  nitric  acid.  If 
to  this  solution  in  nitric  acid  we  add  a  solution  of  ammonium 
molybdate  also  in  nitric  acid,  at  once  or  after  a  time  a  bright- 
yellow  precipitate  of  a  body  called  ammonium  phosphomolybdate 
separates.  In  this  manner  we  can  detect  the  presence  of  phos- 
phorus or  any  of  its  compounds. 


LESSON    XXIV. 
ARSENIC.    As  =  75. 

189.  Arsenic  is   found  associated  with  many  metals,  copper, 
silver,  bismuth,  nickel,  but  it  is  obtained  principally  from  one  of 
its  minerals,  which  contains  also  iron  and  sulphur.     This  mineral 
is  called  mupickel,  and  its  composition  may  be  represented  by  the 
formula  FeSAs.    When  it  is  strongly  heated,  the  arsenic  is  driven 
out,  and  iron  sulphide,  FeS,  remains.     The  operation  is  conducted 
in  clay  retorts,  and  the  arsenic  condenses  in  sheet-iron  receivers. 
This  impure  arsenic  is  generally  sold  under  the  name  cobalt ;  it  is 
purified  by  being  redistilled  out  of  contact  with  air. 

190.  In  a  small  test-tube  we  heat  some  commercial  arsenic,  and 
soon  a  bright  steel-gray  ring  forms  in  the  cooler  part  of  the  tube ; 
after  a  time  the  interior  of  the  ring  becomes  lined  with  small  but 


ARSENIC.  129 

brilliant  metallic  crystals.  This  is  the  appearance  of  arsenic,  but 
its  surface  oxidizes  after  some  exposure  to  the  air,  and  becomes 
tarnished.  The  density  of  arsenic  is  5.7.  It  does  not  melt  when 
heated  ;  it  sublimes ;  but  it  may  be  melted  to  a  transparent  liquid 
by  heating  it  under  pressure.  It  is  insoluble  in  water,  but  is 
slowly  oxidized  by  the  air  dissolved  in  the  water,  and  the  oxide 
dissolves,  rendering  the  water  poisonous.  When  arsenic  is  heated 
in  contact  with  air,  it  volatilizes,  and  its  vapor  is  oxidized  to  white 
arsenious  oxide.  Arsenic  takes  fire  spontaneously  in  chlorine, 
burning  into  arsenic  chloride,  AsCl3,  which  is  a  volatile,  very  poi- 
sonous liquid. 

A  small  quantity  of. arsenic  is  added  to  the  lead  for  making 
shot ;  it  hardens  the  shot,  and  the  interior  of  the  gun-barrel  does 
not  become  coated  with  lead  by  friction  with  that  soft  metal. 

191.  Arsenious  Oxide,  As406. — We  heat  a  very  small  frag- 
ment of  arsenic  in  a  test-tube,  and  presently  a  white  ring  con- 
denses on  the  sides  of  the  tube.  The  arsenic  has  been  oxidized, 
and  the  volatile  oxide  has  condensed  in  the  tube  :  if  we  examine 
the  ring  by  the  aid  of  a  good  microscope,  we  find  that  it  is  com- 
posed of  small,  eight-sided  crystals.  These  are  arsenious  oxide. 
Arsenious  oxide  is  manufactured  in  this  manner,  by  heating 
arsenic  in  contact  with  the  air,  and  the  vapor  is  condensed  either 
in  cool  chimneys  or  in  large  rooms.  As  it  is  a  very  poisonous 
substance,  the  operation  is  conducted  with  all  possible  precaution 
that  the  workmen  may  not  inhale  the  vapors  and  dust. 

When  it  is  freshly  sublimed  in  large  masses,  arsenious  oxide  is 
a  glassy,  transparent,  and  amorphous  solid,  but  it  soon  becomes 
opaque,  and  this  is  due  to  the  formation  of  little  crystals.  It  is 
not  very  soluble  in  water,  and  the  amorphous  form  is  more  sol- 
uble than  the  crystalline  or  opaque  variety.  Amorphous  arsenious 
oxide  dissolves  in  twenty-five  times  its  weight  of  cold  water,  but 
the  crystalline  form  requires  eighty  times  its  weight.  The  solution 
contains  arsenious  acid,  but  when  we  evaporate  the  liquid  and  try 
to  separate  this  acid,  it  is  again  decomposed  into  arsenious  oxide 

and  water. 

As*0«  +  6H20         =          4H3AsO* 

Arsenious  oxide.  Water.  Arsenious  acid. 


130  LESSONS    IN    CHEMISTRY. 

Because  arsenious  oxide  is  frequently  the  cause  of  intentional 
or  accidental  poisoning,  it  is  important  that  we  shall  be  able  to 
recognize  it;  but  we  will  better  understand  its  tests  when  we  have 
learned  something  of  the  other  compounds  of  arsenic. 

192.  Arsenic  Oxide  and  Acids,— When  arsenic  or  arsenious 
acid  is  boiled  with  nitric  acid,  it  is  oxidized  just  as  phosphorus 
was  oxidized,  and  the  ortho-arsenic  acid  formed  corresponds  ex- 
actly to  orthophosphoric  acid.     It  contains  H3AsO*.     When  it  is 
heated  to  150°.  it  is  decomposed  like  orthophosphoric  acid,  and 
pyroarsenic  acid,  H4As207,  is  formed.     This  also  is  decomposed 
at  200°,  yielding  metarsenic  acid,  HAsO3,  which  when  heated  to 
redness  loses  the  elements  of  water,  and  leaves  arsenic  oxide,  As205. 

2H3AsO*    =     H4As2Q7     +     H'O        IVAsW     =     2HAs03     +     H20 
2HAs03    =     As2Q5     +     H2Q 

193.  We  boil  a  few  grains  of  arsenious  oxide  with  a  few  drops 
of  nitric  acid  in  a  test-tube,  and  when  the  last  particle  of  the 
solid  disappears,  we  carefully  neutralize  the  liquid  with  ammonia. 
Now  when  we  add  some  silver  nitrate  solution,  a  brick-red  pre- 
cipitate of  silver  arsenate  is  formed. 

(NH4)3AsO*          +        3AgN03        =        AgSAsO*       -f        3NH*N03 
Ammonium  arsenate.  Silver  nitrate.  Silver  arsenate.     Ammonium  nitrate. 

194.  Arsenic  Sulphides. — In  a  test-tube  of  hard  glass  we 
melt  together  some  powdered  arsenic  mixed  with  a  little  more 
than  half  its  weight  of  sulphur.     After  cooling,  the  liquid  solidi- 
fies to  a  red  mass  of  arsenic  disulphide,  As2S2.     This  substance 
is  commonly  called  realgar.     It  is  found  as  a  mineral  in  trans- 
parent red  prisms.     It  is  insoluble  in  water.     When  heated  in 
the  air,  both  its  arsenic  and  sulphur  burn,  yielding  arsenious  oxide 
and  sulphur  dioxide. 

In  another  test-tube  we  melt  a  mixture  of  powdered  arsenic 
with  about  two-thirds  its  weight  of  sulphur.  When  this  tube 
cools,  we  find  in  it  yellow  arsenic  trisulphide,  As2S3,  generally 
called  orpiment.  This  sulphide  also  is  found  as  a  mineral.  It  is 
insoluble  in  water,  but  if  boiled  for  a  long  time  with  that  liquid 
it  is  decomposed,  yielding  hydrogen  sulphide  and  arsenious  acid. 
6H2Q  =  2H3As03  +  3H2S 


TESTS   FOR   ARSENIC. 


131 


Conversely,  by  passing  hydrogen  sulphide  through  a  solution 
of  arsenious  oxide  to  which  a  drop  of  hydrochloric  acid  has  been 
added,  yellow  arsenious  sulphide  is  precipitated. 

195.  Tests  for  Arsenic. — Arsenious  oxide  and  some  of  its 
compounds  are  the  usual  forms  in  which  we  must  identify  arsenic. 
In  a  porcelain  evaporating  dish  we  heat  some  pure  water,  and 
when  it  boils  we  add  a  few  drops  of  hydrochloric  acid,  and  then 
put  in  a  thin  strip  of  bright  copper.    The  metal  does  not  tarnish  ; 
but  when  we  add  to  the  boiling  liquid  a  little  of  any  solution  con- 
taining arsenic,  the  copper  soon  becomes  coated  with  a  steel-gray 
or  even  black  deposit,  which  is  a  compound  of  copper  and  arsenic. 
This  is  called  Reinsch's  test.     We  take  this  slip  of  copper  from 
the  liquid,  wash  it 

in  pure  water,  and 
carefully  dry  it  be- 
tween folds  of  warm 
filter-paper.  Then 
we  cut  it  into  sev- 
eral very  narrow 
slips,  and  put  one 
or  two  of  these  in  a 
little  tube  drawn  out 
and  sealed  at  one 
end.  We  cover  this 
piece  of  copper  with  some  warm  charcoal  powder,  and  then  heat 
the  end  of  the  tube.  The  heat  drives  the  arsenic  away  from  the 
copper,  and  the  charcoal  prevents  the  vapor  from  becoming  oxi- 
dized, so  that  a  gray  or  black  mirror  of  arsenic  condenses  in  the 
nearest  cool  part  of  the  tube  (Fig.  63). 

196.  In  another  similar  tube  we  put  another  piece  of  our  coated 
copper  foil,  and  heat  it  alone.     In  this  case  the  arsenic  vapor  be- 
comes oxidized  by  the  air  in  the  tube,  and  white  arsenious  oxide 
is  deposited  in  minute  octahedral  crystals  that  we  may  recognize 
when  we  examine  the  tube  under  the  microscope  (Fig.  64),    Were 
we  to  break  off  the  portion  of  the  tube  containing  this  deposit, 
and  boil  it  with  a  very  little  water  in  another  tube,  we  would 


FIG.  63. 


132  LESSONS    IN    CHEMISTRY. 

obtain  a  solution  of  arsenious  acid,  with  which  we  could  make  the 
next  tests ;  these,  however,  we  will  make  with  larger  quantities  of 
the  substance. 

197.  To  a  solution  of  arsenious  acid  in  a  test-tube,  we  add  a 
drop  of  ammonia,  and  then  some  silver  nitrate  solution.    A  canary- 
yellow  precipitate  of  insoluble  silver  arsenite  is  formed. 

(NH^HAsO3        +     2AgN03     =     2NH*N03     +       Ag'IIAsO3 
Ammonium  arsenite.  Silver  arsenite. 

198.  To  a  similar  solution,  treated  with  a  little  ammonia,  we 

add  cupric  sulphate  dissolved  in  water. 
An  apple-green  precipitate  of  cupric 
arsenite,  CuHAsO3,  is  thrown  down. 

199.  In   another   tube  we   acidulate 
.some  arsenious  acid  with  a  drop  of  hy- 
drochloric acid,  and  then  pass  hydrogen 
sulphide  through  the  liquid.     A  bright 
yellow  precipitate  of  arsenic  trisulphide 
is  formed. 

200.  When  arsenious  acid  is  poured 

into  a  bottle  in  which  hydrogen  is  being  generated,  the  nascent 
hydrogen,  that  is,  the  free  atoms  of  hydrogen  which  have  not 
exhausted  part  of  their  energy  by  combining  to  form  molecules, 
will  reduce  or  take  away  oxygen  from  the  arsenious  acid,  and 
combine  with  the  arsenic,  forming  an  exceedingly  poisonous  gas, 
of  which  we  must  be  careful  not  to  inhale  the  least  quantity.     It 
is  called  hydrogen  arsenide.     Its  molecule  contains  AsH3. 

H3As03     +     6H     =     3H20     +     AsH3 

We  have  prepared  a  hydrogen-bottle  with  a  long  jet  (Fig.  65), 
and,  while  the  hydrogen  is  burning  with  its  pale  flame  at  this  jet, 
we  pour  through  the  funnel-tube  a  few  drops  of  a  solution  of 
arsenious  oxide.  In  a  few  moments  the  flame  becomes  bluish  and 
elongated.  Hydrogen  arsenide  is  burning,  and  the  arsenic  oxidizes 
to  arsenious  oxide,  producing  a  white  smoke.  In  this  flame,  and 
close  to  the  jet,  we  hold  a  plate  or  piece  of  cold  porcelain,  which 
will  prevent  the  arsenic  from  getting  enough  oxygen  to  become 
oxidized.  We  see  a  dark  spot  of  arsenic  forming,  and  we  make 


TESTS   FOE   ARSENIC. 


133 


several  of  these  spots  on  different  portions  of  the  plate.    This  is 

called  Marsh's  test.    If  with  a  lamp  we  heat  the  tube  of  the  long 

jet,  the  hydrogen  arsenide 

will    be    decomposed    by 

the    heat,   and   the   dark 

ring  of  arsenic  deposited 

in  the  cooler  part  of  the 

tube    may  be    afterwards 

tested  as  we  have  already 

studied. 

201.  We     connect     a 
little  bent  tube  with  our 
jet,  and  pass  the  gas  into 
some  silver  nitrate  solution 
in  a  test-tube  ;  a  black  de- 
posit of  silver  separates, 

and     arsenious     acid     is  FIG.  05. 

formed  in  the  solution. 

AsIP     +     6AgN03     -f     3H20     =     H3As03     +     6HN03     +     6Ag 
We  filter  the  liquid  from  the  silver,  and  add  a  drop  of  ammonia ; 
if  all  of  the  silver  nitrate  has  not  been  decomposed,  a  yellow 
precipitate  of  silver  arsenite  is  formed.    We  may  be  obliged  to  add 
a  few  more  drops  of  silver  nitrate  (§  197). 

202.  Now  we  touch  one  of  the  spots  on  our  plate  with  a  drop 
of  strong  nitric  acid.     The  spot  disappears :  we  add  a  small  drop 
of  ammonia,  and  cautiously  warm  the  plate  until  it  is  dry.    Then 
we  touch  it  with  a  drop  of  silver  nitrate,  and  it  becomes  brick-red 
iroiii  the  formation  of  silver  arsenate  (§  193). 

All  of  these  tests  enable  us  to  recognize  arsenic  with  certainty; 
they  are  applied  to  substances  which  are  extracted  from  the  body 
in  cases  of  supposed  poisoning. 

The  green  coloring  matters  known  as  Scheele's  green  and  Paris 
green  are  compounds  containing  arsenic  and  copper:  they  are 
exceedingly  poisonous. 


134  LESSONS    IN   CHEMISTRY. 


LESSON    XXV. 

ANTIMONY.     Sb  (Stibium)  =  120. 

203.  Antimony  is  found  principally  in  combination  with 
sulphur  in  a  grayish-black  mineral,  stibnite,  Sb2S3.  This  sul- 
phide is  quite  fusible,  and  it  is  separated  from  the  earthy  matters 
with  which  it  is  mixed,  and  which  are  called  the  gangue,  simply 
by  heating  the  ore ;  the  antimony  sulphide  melts  and  runs  out.  The 
easiest  method  of  obtaining  antimony  from  this  sulphide  is  to  mix 
the  powdered  sulphide  with  scrap  iron  and  heat  the  mixture  to 
redness  in  a  crucible.  Iron  sulphide  and  antimony  are  formed, 
and  the  latter,  being  the  heavier,  collects  at  the  bottom,  where  we 
find  it  as  a  bright  button-shaped  lump  when  we  break  the  cold 
crucible.  The  cheapest  method,  however,  is  to  roast  the  powdered 
sulphide ;  that  is,  heat  it  in  the  air ;  most  of  the  sulphur  is  then 
oxidized  to  sulphur  dioxide,  which  passes  off,  and  most  of  the  anti- 
mony is  converted  into  antimonous  oxide.  The  roasted  mass  is 
then  mixed  with  charcoal,  and  the  mixture  moistened  with  a  solu- 
tion of  sodium  hydroxide,  after  which  it  is  heated  in  crucibles. 
The  carbon  removes  the  oxygen  from  the  antimony  oxide,  and  the 
sodium  hydroxide  removes  the  sulphur  from  the  antimony  sulphide 
still  present.  The  sodium  sulphide  produced  forms  a  slag  which 
floats  on  the  surface  of  the  melted  antimony. 

PROPERTIES. — Antimony  is  a  very  brilliant,  white  substance, 
having  a  high  metallic  lustre.  It  is  very  brittle,  and  breaks 
in  shining  layers :  it  is  said  to  have  a  laminated  structure.  Its 
density  is  6.7.  It  melts  at  450° ;  when  a  considerable  quantity 
of  it  is  melted  in  a  crucible  and  allowed  to  cool  quietly  until 
a  crust  forms  on  the  surface,  if  we  make  a  hole  in  this  crust  and 
pour  out  the  still  molten  interior,  the  crucible  will  be  found  to  be 
lined  with  small  shining  crystals. 

When  antimony  is  heated  in  the  air,  it  is  oxidized  to  antimo. 
nous  oxide,  Sb406.  We  have  already  seen  that  antimony  burns 


ANTIMONY.  135 

spontaneously  when  thrown  into  chlorine.  It  combines  with 
the  chlorine,  forming  a  trichloride,  SbCP,  and  a  pentachloride, 
SbCP. 

Antimony  enters  into  the  composition  of  several  alloys.  Type- 
metal  contains  twenty  per  cent,  of  antimony  and  eighty  per  cent, 
of  lead.  Lead  is  too  soft  for  type,  and  it  does  not  take  sharp  im- 
pressions of  moulds :  the  antimony  renders  the  metal  hard,  and 
causes  it  to  expand  on  solidifying,  so  filling  every  line  of  the 
mould.  Britannia  metal  also  contains  antimony. 

204.  Antimony  Chlorides. — By  distilling  antimony  trisulphide  with  hydro- 
chloric acid,  and  collecting  apart  the  product  which  passes  after  the  condensed 
liquid  begins  to  crystallize  in  the  neck  of  the  retort,  antimony  trichloride,  SbCl3, 
is  obtained  as  a  transparent,  colorless  solid,  melting  at  73°,  and  boiling  at  230°. 
It  is  soluble  in  dilute  hydrochloric  acid,  but  when  the  solution  is  diluted  with 
water,  an  insoluble  oxychloride,  SbOCl,  is  thrown  down,  while  hydrochloric 
acid  is  formed.     Antimony  pentachloride,  SbCl5,  is  a  volatile,  yellow  liquid, 
formed  by  the  action  of  an  excess  of  chlorine  on  antimony  or  the  trichloride. 

205.  Antimony  Oxides. — Antimonons  oxide,  Sb*06,  is  made  by  heating  anti- 
mony to  redness  in  open  crucibles  ;  after  cooling,  the  latter  are  found  lined  with 
shining,  needle-like  crystals  of  the  oxide,  which  corresponds  in  composition  to 
arsenious  oxide.     When  antimony  is  boiled  with  strong  nitric  acid,  it  is  con- 
verted into  metantimonic  acid,  HSbO3;  by  heating  to  about  275°  this  is  de- 
composed, yielding  antimony  pentoxide,   Sb205;    at   higher  temperatures    it 
breaks  up  into  the  tetroxide,  Sb20*,  and  oxygen.     There  is  also  a  pyranti- 
monic  acid,  H4Sb207,  but  there  is  no  orthantimonic  acid  of  the  composition 
IPSbO4. 

Antimony  tetroxide  is  also  formed  by  heating  antimonous  oxide  in  the  air. 
It  is  white  powder  and  insoluble  in  water. 

206.  Antimony  Trisulphide,  Sb2S3,  is  the  grayish-black  min- 
eral, called  stibnite,  from  which  we  have  already  learned  that 
antimony  is   obtained.     It  is   a  heavy,   crystalline  substance, 
having  a  marked  metallic  appearance.     This  same   sulphide 
may  be  obtained  in  another  form.     Through  a  solution  of  anti- 
mony trichloride   we   pass  hydrogen  sulphide ;    an   amorphous, 
orange-colored  precipitate  is  formed,  and  this  is  antimony  trisul- 
phide. 

2SbCl3  +  3H2S        =  Sb2S3  +         6HC1 

Antimony  trichloride.  Antimony  trisulphide. 

207.  When  a  solution  containing  antimony  is  introduced  into 
a  bottle  in  which  hydrogen  is  being  generated,  some  of  the  hydro- 


136  LESSONS    IN    CHEMISTRY. 

gen  combines  with  the  antimony,  producing  a  gas,  hydrogen  anti- 
monide.  Although  this  gas  has  not  been  obtained  in  a  pure  state, 
being  very  easily  decomposed,  enough  has  been  learned  about  it 
to  show  that  it  has  the  composition  SbH3.  It  causes  the  hydro- 
gen to  burn  with  a  bluish  flame,  somewhat  like  that  of  hydrogen 
arsenide,  and  it  also  produces  dark  spots  on  a  piece  of  porcelain 
held  in  the  flame,  as  well  as  rings  in  the  heated  tube  (§  200)  ;  but 
here  the  resemblance  with  arsenic  ceases.  When  the  spots  are 
oxidized  by  nitric  acid  and  then  treated  with  silver  nitrate,  no 
brick-red  color  is  produced.  When  the  gas  is  passed  through 
silver  nitrate  solution,  a  dark  compound  of  silver  and  antimony  is 
precipitated,  and,  as  the  clear  liquid  then  contains  only  nitric  acid, 
it  cannot  give  a  precipitate  when  neutralized  with  ammonia 
(§§  200-202). 

208.  When  we  compare  the  compounds  of  nitrogen,  phosphorus,  arsenic, 
and  antimony,  we  find  that  the  atoms  of  these  elements  are  almost  alike  as 
far  as  their  power  of  combining  is  concerned.     One  atom  of  each  will  combina 
with  three  atoms  of  hydrogen,  and  we  then  have  formed  the  four  gases, 

NH»  PEP  AsH3  SbH3 

Their  more  important  compounds  with  chlorine  show  the  same  similarity  : 
NCI3  PCI3  AsCl3  SbCl3 

But,  in  addition  to  these  chlorides,  phosphorus  and  antimony  form  penta- 
chlorides,  PCI5  and  SbCl5.  Each  of  the  four  elements  has  a  trioxide  and  a 
pentoxide,  and  from  each  of  the  pentoxides  is  derived  an  acid  containing  one 
atom  of  hydrogen,  one  atom  of  the  element,  and  three  atoms  of  oxygen : 

UNO3  HPO3  HAsO3  HSbO3 

In  addition,  phosphorus  and  arsenic  form  the  ortho-acids,  H3PO*  and 
H3AsO*,  while  phosphorus,  arsenic,  and  antimony  form  the  pyro-acids,  H4P207, 
H*  A  8*07,  and  H^Sb'O*. 

These  similarities  and  many  others  enable  us  to  group  together  the  four  ele- 
ments in  a  natural  class;  since  in  their  compounds  one  atom  of  either  of  the 
class  has  a  combining  power  equal  to  that  of  three  or  of  five  atoms  of  hydro- 
gen, we  may  call  the  class  the  group  of  triatomic  or  pentatomic  non-metals. 

209.  There  are  three  other  elements  which  would  be  placed  in  the  class  that 
we  have  just  considered,  but  they  occur  in  such  small  quantities,  although 
widely  distributed,  that  we  can  only  mention  their  names.     They  are  vana- 
dium, niobium,  and  tantalum.     They  are  found  in  the   minerals  vanadinite, 
coluiubite,  and  some  others. . 


BORON.  137 


LESSON    XXVI. 

BORON.    B=  ii. 

210.  The  well-known  substance,  borax,  is  a  compound  of  the 
element  boron.     To  a  saturated  solution  of  borax  we  add  some 
sulphuric  acid :  soon  there  separates  a  deposit  composed  of  small 
white  flakes.     If  we  filter  these  flakes  from  the  liquid,  and  dry 
them,  we  have  pearly  white  scales  which  feel  greasy  like  soap 
when  we  take  them  between  the  fingers.     This  substance  is  boric 
acid ;  it  contains  H3B03.     If  we  heat  it  red  hot  in  a  platinum 
crucible,  it  decomposes  and  leaves  boric  oxide,  B203. 

2H3B03  =  3H2Q  +  B2Q3 

When  this  boric  oxide  is  mixed  with  pieces  of  sodium,  some 
common  salt  being  added  to  make  the  mixture  melt  more  readily, 
and  heated  to  bright  redness  in  a  covered  iron  crucible,  sodium 
borate  and  boron  are  formed. 

3Na2         +         2B203        =         2Na3B03         +         B* 
Boric  oxide.  Sodium  borate. 

After  the  crucible  has  cooled,  the  fused  mass  is  treated  with  dilute 
hydrochloric  acid,  which  dissolves  the  sodium  borate,  leaving  the 
boron  as  a  dark-brown  or  olive  powder. 

Boron  is  amorphous,  infusible,  insoluble  in  water.  When  it  is 
heated  in  the  air  or  in  oxygen,  it  takes  fire  and  burns  to  boric 
oxide.  It  is  one  of  the  few  elements  which  combine  directly  with 
nitrogen  :  at  a  red  heat  in  an  atmosphere  of  nitrogen  it  is  con- 
verted into  boron  nitride,  BN.  It  also  burns  in  nitrogen  dioxide 
when  heated  in  that  gas,  and  forms  a  mixture  of  boron  nitride  and 
boric  oxide. 

211.  Boric  Oxide. — Boric  oxide,  of  which  we  have  already 
learned  the  manner  of  formation,  is  a  hard,  transparent,  glass-like 
substance.     It  melts  at  a  red  heat,  and  when  melted  has  the  prop- 
erty of  dissolving  many  metallic  oxides,  which  communicate  vari- 
ous colors  to  the  cooled  oxide.     We  heat  to  redness  the  end  of  a 


138  LESSONS   IN   CHEMISTRY. 

small  platinum  wire,  and,  when  it  is  very  hot,  we  dip  it  into  some 
boric  acid  or  powdered  boric  oxide ;  on  again  heating  this  in  the 
flame,  it  melts  to  a  sort  of  glass  bead,  which  is  perfectly  trans- 
parent and  colorless  when  cold.  We  now  dip  it  into  a  solution 
of  cobalt  chloride,  and  again  heat  it :  when  it  cools,  the  bead  has 
a  blue  color.  This  blue  color  is  given  by  the  cobalt.  As  many 
metals  give  peculiar  colors  to'  such  beads  of  boric  oxide,  we  have 
in  that  substance  a  valuable  reagent  to  aid  in  the  detection  of  the 
metals. 

Boric  oxide  is  not  reduced  by  heating  it  with  charcoal,  but 
when  chlorine  is  passed  over  a  red-hot  mixture  of  boric  oxide  and 
charcoal,  carbon  monoxide,  CO,  is  disengaged,  together  with  the 
vapor  of  a  very  volatile  liquid,  boron  chloride,  BC13. 

B203        +        30        +        3C12        =        2BC13        +        SCO 
Boric  oxide.  Boron  chloride. 

212.  When  boric  oxide  is  melted  with  the  metal  aluminium,  a 
part  of  the  metal  is  oxidized,  and  another  part  combines  with  the 
boron  from  which  the  oxygen  was  removed ;  there  is  so  formed  a 
complex  compound  of  boron  and  aluminium,  which  separates  in 
small  crystals  when  the  mass  cools.     As  these  crystals  are  mixed 
with  the  excess  of  solid  aluminium,  we  must  remove  that  metal 
by  boiling  in  dilute  hydrochloric  acid.     Small  octahedral  crystals 
remain  undissolved :  they  were  long  regarded  as  crystallized  boron. 
Their  composition  is  not  always  the  same.     Their  color  is  yellow, 
red,  or  black :  their  density  is  about  2.6,  and  they  are  almost  as 
hard  as  diamond :  they  will  scratch  rubies,  and  have  sometimes 
been  employed  for  polishing  precious  stones. 

213.  Boric  Acid  and  Borates. — We  have  already  seen  that 
boric  acid  may  be  formed  by  the  action  of  sulphuric  acid  on  borax. 
It  dissolves  in  about  twenty-five  times  its  weight  of  cold  water,  and 
the  solution  is  not  very  strongly  acid ;  it  changes  blue  litmus  to  a 
wine  color. 

It  is  found  in  nature  in  the  craters  of  some  volcanoes.  In  nu- 
merous localities  in  Tuscany  gases  issue  from  cracks  in  the  earth, 
and  these  volcanic  gases  contain  boric  acid.  To  obtain  this  body 


BOEIC   ACIDS. — BORAX.  139 

the  gas  is  caused  to  bubble  tbrough  the  water  of  little  lakes,  and 
when  the  water  is  evaporated,  the  boric  acid  is  left. 

Boric  acid  is  tribasic:  when  it  is  heated  to  100°,  it  is  decom- 
posed into  water  and  metaboric  acid. 

H3BQ3        =  HBO2  +         H20 

Boric  acid.  Metaboric  acid. 

If  the  latter  be  heated  to  140°  for  a  time,  it  is  further  decom- 
posed into  another  acid,  called  tetraboric. 

4HB02        =         H2B*07         +         H*0 
Metaboric  acid.         Tetraboric  acid. 

Tetraboric  acid  is  that  to  which  correspond  borax  and  the 
common  borates.  In  borax,  which  is  sodium  tetraborate,  both  of 
the  hydrogen  atoms  are  replaced  by  sodium. 

214.  BORAX,  Na2B407,  was  for  a  long  time  obtained  princi- 
pally from  Asia  and  from  the  boric  acid  of  Tuscany,  but  within 
recent  years  the  bulk  of  the  commercial  article  has  been  made 
from  the  borate  of  calcium,  of  which  large  deposits  occur  in  Cali- 
fornia, Peru,  and  Asia  Minor.  This  mineral,  known  as  coleman- 
ite  or  pandermite,  is  converted  into  the  sodium  salt  by  treating 
it  with  a  boiling  solution  of  sodium  carbonate.  When  a  very 
concentrated  solution  of  borax  cools,  it  deposits,  between  70° 
and  56°,  octahedral  crystals  in  which  one  molecule  of  borax 
is  combined  with  five  molecules  of  water  of  crystallization ; 
but  below  56°  it  deposits  prismatic  crystals  containing  ten 
molecules  of  water.  The  borax  of  commerce  is  generally  pre- 
pared in  the  latter  form.  Prismatic  borax  dissolves  in  - 
twelve  times  its  weight  of  cold,  or  twice  its  weight  of  boiling 
water. 

When  borax  is  heated,  it  loses  its  water  of  crystallization  more 
quickly  than  that  water  can  evaporate ;  the  borax  is  consequently 
dissolved  in  the  separated  water :  it  is  said  to  melt  in  its  water  of 
crystallization.  As  the  water  is  driven  off  by  the  heat,  it  causes 
the  borax  to  swell  up,  until  it  becomes  a  dry,  white,  and  very 
light  mass.  When  this  is  still  further  heated,  it  melts  to  a  sort  of 
glass,  which  possesses  the  same  property  of  dissolving  metallic 
oxides  that  we  noticed  in  fused  boric  oxide.  For  this  reason  borax 


140  LESSONS    IN    CHEMISTRY. 

is  often  used  in  analysis  instead  of  boric  oxide.  Because  borax 
dissolves  metallic  oxides,  it  is  useful  in  brazing  and  welding.  The 
surfaces  of  metal  to  be  welded  together  become  oxidized  at  the 
high  temperature  necessary,  and  the  oxide  would  prevent  their 
union :  a  little  borax  sprinkled  on  the  hot  surfaces  dissolves  the 
oxide,  and  the  liquid  is  squeezed  out  when  they  are  pressed 
together,  leaving  clean  surfaces  which  readily  unite. 

215.  We  dissolve  in  alcohol  a  little  boric  oxide,  or  some  borax 
to  which  a  few  drops  of  sulphuric  acid  have  been  added.  On 
lighting  this  alcohol,  it  burns  with  a  green  flame.  This  test  helps 
us  to  recognize  boric  acid  or  a  borate. 


LESSON    XXVII. 
SILICON.     Si  =  28. 

216.  Silicon  is  one  of  the  most  abundant  elements.  In  the 
form  of  oxide  it  exists  in  quartz,  and  forms  part  of  nearly  all 
rocks  and  of  many  minerals.  It  is  obtained  in  the  free  state  by 
heating  a  mixture  of  powdered  quartz  and  magnesium  powder. 

SiO2      +      2Mg      =      2Si      +      2MgO. 

After  washing  the  residue  with  dilute  hydro- 
chloric acid,  in  which  the  magnesium  oxide 
dissolves,  the  silicon  remains  as  an  amorphous 
brown  powder.  Two  crystallized  modifications 
of  silicon  have  also  been  obtained. 

217.  Silicic  Oxide,  SiO2.— This  compound, 
generally  called  silica,  is  found  in  many  forms. 
Crystallized,  it  constitutes  the  various  kinds  of 
quartz,  such  as  rock  crystal  and   amethyst ; 
FIG"  66  agate,  flint,  and  chalcedony  are  other  varieties. 

Sandstones  and  sand  are  also  silica.  Pure 
quartz  or  rock  crystal  is  colorless.  It  forms  hexagonal  prisms 
terminated  by  six-sided  pyramids,  and  the  angles  are  often 


SILICA.— GLASS.  141 

curiously  modified  (Fig.  G6).  Its  density  is  2.65.  It  is  in- 
soluble in  water ;  and  can  be  melted  only  in  the  oxyhydro- 
gen  flame  and  in  the  electric  furnace.  It  is  not  reduced  by 
hydrogen,  and  by  carbon  only  with  the  aid  of  the  electric 
arc.  It  is  scarcely  affected  by  any  chemical  agents  at  ordi- 
nary temperatures,  with  the  exception  of  hydrofluoric  acid 
(§  93).  When  it  is  strongly  heated  with  alkaline  hydroxides 
or  carbonates,  it  enters  into  combination  with  the  metal,  form- 
ing silicates,  and  these  silicates  are  capable  of  dissolving  silica 
at  very  high  temperatures.  When  the  mass  cools,  it  constitutes 
glass,  and  the  properties  of  the  glass  depend  upon  the  proportions 
of  silica  and  alkaline  hydroxide  or  carbonate  employed.  If  there 
be  a  large  proportion  of  the  alkali,  the  glass  is  soluble  in  water, 
and  soluble  glass  is  made  by  fusing  silica  with  either  potassium  or 
sodium  carbonate, — generally  the  latter,  because  it  is  cheaper.  The 
solution  of  this  substance  hardens  as  the  water  evaporates,  and  is 
employed  as  a  cement  and  in  making  artificial  stone. 

218.  Ordinary  glass  is  made  by  melting  in  large  clay  pots,  or 
in  furnaces  of  peculiar  construction,  a  mixture  of  fine  white  sand, 
sodium  carbonate,  and  lime.     If  it  is  desired  that  the  glass  shall 
not  soften  at  a  high  temperature,  potassium  carbonate  is  used  in- 
stead of  sodium  carbonate.    When  the  bubbles  of  carbon  dioxide, 
which  are  given  off  from  the  carbonate  employed,  have  escaped 
from  the  pasty  liquid,  the  workman  takes  out  some  of  the  molten 
metal,  as  it  is  called,  on  the  end  of  a  long  iron  tube,  through  which 
he  blows  air  into  this  lump  of  soft  glass ;  if  the  lump  be  in  a 
bottle- mould,  the  glass  takes  the  form  of  the  mould.     Common 
window-glass  is  made  by  blowing  large  globes  which  are  drawn 
out  into  cylinders  by  their  own  weight  as  they  hang  on  the  blow- 
pipe.    The  cylinders  when  cold  are  cut  open  their  whole  length, 
and  are  then  heated  in  a  furnace,  and  when  soft  enough  are  unrolled 
into  sheets. 

219.  CRYSTAL,  the  very  heavy  and  perfectly  colorless  glass 
from  which  cut-glass  objects  are  made,  contains  lead  silicate,  which 
is  formed  by  adding  red  lead  to  the  mixture  of  alkaline  carbonate 
and  sand  before  fusing  it.     A  little  lead  is  often  used  in  making 
common  glass.     The  dark-green  color  of  bottle-glass  is  caused  by 


142  LESSONS    IN    CHEMISTRY. 

the  presence  of  iron  in  the  sand  used,  and,  in  general,  colored 
glasses  owe  the  color  to  the  presence  of  certain  metals,  as  we  shall 
in  time  learn.  Plate-glass  is  cast  on  polished  metallic  tables,  and 
while  still  soft  is  rolled  out  by  heavy  rollers,  as  dough  is  rolled. 
It  is  afterwards  ground  flat  and  polished  by  machinery.  Tumblers, 
goblets,  and  like  objects  are  made  by  pressing  the  soft  glass  into 
moulds. 

220.  By  the  action  of  energetic  acids  the  alkaline  metal  is  at 
once  removed  from  soluble  glass.     We  pour  into  a  saucer  some 
thick  solution  of  sodium  silicate  (sodium  soluble  glass),  and  on 
the  surface  of  this  we  carefully  pour  some  hydrochloric  acid ;  on 
pouring  these  liquids  from  a  little  height  into  another  saucer,  as 
they  run  out  they  mix  on  the  edge,  and  the  silica  which  is  sepa 
rated  from  the  sodium  hangs  on  the  saucer  in  long  icicle-like 
masses. 

In  a  beaker  glass  we  maue  a  rather  dilute  solution  of  sodium 
silicate,  and  gradually  mix  it  with  dilute  hydrochloric  acid.  Here 
also  sodium  chloride  is  formed  by  the  action  of  the  hydrochloric 
acid,  but  no  silica  is  precipitated.  Where  is  it  ?  It  must  be  in 
the  solution,  and  it  exists  there  in  the  form  of  soluble  silicic  acid. 
It  may  be  separated  from  the  sodium  chloride  by  a  process  called 
dialysis ;  the  sodium  chloride  is  a  crystalline  body,  but  silicic  acid 
is  *  amorphous.  When  a  solution  containing  a  mixture  of  crys- 
talline and  amorphous  bodies  is  put  in  a  dialyser, — which  is  any 
glass  vessel  of  which  the  bottom  is  cut  out  and  replaced  by  a  piece 
of  parchment  paper  firmly  tied  on, — and  the  dialyser  is  placed  in  a 
vessel  of  water,  the  crystalline  substance  passes  through  the  mem- 
brane, while  the  amorphous  body  remains  in  the  interior.  Then 
when  we  pour  our  solution  containing  silicic  acid  into  a  dialyser, 
and  set  the  dialyser  in  a  vessel  of  water,  after  a  time  we  find  the 
silicic  acid  alone  in  the  water  of  the  inner  vessel.  This  acid  prob- 
ably has  the  composition  H4Si04  =  2H20  -f  SiO2.  If  we  set 
aside  for  a  few  days  the  beaker  containing  it,  the  whole  liquid  is 
converted  into  a  jelly.  The  silicic  acid  has  become  an  insoluble 
silicic  hydrate,  H2Si03  =  H20  -f  SiO2. 

221.  Hydrofluosilicic  Acid. — We  have  seen  how  hydrofluoric 


IIYDROFLUOSILICIC    ACID. 


143 


acid  attacks  silica  (§  93).  We  put  into  a  glass  flask  an  intimate 
mixture  of  calcium  fluoride  (fluor-spar)  with  fine  quartz  sand  and 
enough  sulphuric  acid  to  make  a  creamy  liquid.  We  have  adapted 


tube  and  a  delivery- 
of  a  tall  jar  where  it 


to  our  flask  a  cork  having  a  safety- 
tube  which  may  pass  to  the  bottom 
dips  into  some  mercury.  On 
this  mercury  we  pour  some 
water,  and,  as  our  gas  must 
overcome  the  pressure  of  this 
water  and  the  mercury,  we 
pour  a  little  mercury  in  the 
safety-tube  (Fig.  67).  We 
now  gently  heat  our  flask, 
and  as  each  bubble  of  gas 
passes  through  the  mercury 
and  touches  the  water,  a  ge- 
latinous deposit  of  silicic  hy- 
drate is  produced ;  we  use 
the  mercury  in  order  that 
the  delivery-tube  may  not 

become  stopped  by  this  deposit.  In  the  reaction  which  is  taking 
place,  the  hydrofluoric  acid  which  is  eliminated  from  the  fluor- 
spar and  sulphuric  acid  at  once  acts  upon  the  silica,  forming  silicon 
fluoride,  SiF*.  This  is  the  gas  which  comes  from  the  flask. 


FIG.  67. 


2CaF2     +      2H2SO* 
Calcium  fluoride. 


SiO2     =     2CaS04   +    2H20    +     SiF* 
Silicic  oxide.  Silicon  fluoride. 


When  this  gas  comes  in  contact  with  water,  a  reaction  takes 
place,  in  which  silicic  hydrate,  H2Si03,  is  formed,  together  with  a 
kras  which  dissolves  in  the  water  and  is  called  hydrofluosilicic  acid. 
It  is  a  double  fluoride  of  silicon  and  hydrogen. 


3S1F*      + 

Silicon  fluoride. 


3H2Q       =      H2Si03 


2(SiF*.2HF) 
Hydrofluosilicic  acid. 


The  strong  solution  of  this  gas  is  a  highly  acid  liquid,  and  is 
valuable  as  a  test  for  the  metals  potassium  and  sodium,  which  it 
precipitates  from  solutions  of  their  salts.  To  a  solution  of  potas- 
sium nitrate  we  add  some  of  our  filtered  liquid,  and  at  once  an 


144  LESSONS    IN    CHEMISTRY. 

insoluble  double  fluoride  of  potassium  and  silicon  is  precipitated, 
while  nitric  acid  now  exists  in  the  solution. 

2KN03       +        SiF*.2HF        =       2HN03        +         SiF*.2KF 

Hydrofluosilicic  acid.  Silicopotassiuni  fluoride. 


LESSON    XXVIII. 
CARBON.    C  =  12. 

222.  When  we  compare  together  a  diamond,  a  piece  of  char- 
coal, and  a  piece  of  graphite  from  a  lead-pencil,  we  would  not 
suppose  that  they  have  many  properties  in  common  ;  much  less 
would  we  think  that  they  are  different  forms  of  the  same  sub- 
stance.    Yet  this  is  the  case.     They  are  only  varieties  of  the  ele- 
ment carbon.     Charcoal  is  formed  by  the   decomposition  of 
various  compounds  of  carbon,  and  the  other  two  modifications 
have  been  obtained  from  solutions  of  carbon  in  molten  metals. 
When  charcoal  is  dissolved  in  molten  iron,  part  of  the  carbon 
deposits  upon  cooling,  usually  in  the  form  of  graphite,  but  when 
the  mass  is  heated  to  about  3000°  in  the  electrical  furnace, 
and  then  suddenly  cooled,  the  carbon  is  partly  converted  into 
diamond.     We  may  say,  then,  that  there  are  three  modifications 
of  carbon,  two  crystalline   (diamond  and  graphite),  and  one 
amorphous,  which  latter  includes  all  the  varieties  of  charcoal. 

223.  DIAMOND. — This  is  the  hardest  of  substances :  it  can  be 
cut  and  polished  only  by  its  own  dust.     It  is  found  crystallized  in 
regular  octahedra  and   forms  of  twelve,  twenty-four,  and  forty- 
eight  faces,  and  the  faces  are  usually  curved   (Fig.  68).     The 
most  highly  prized  varieties  are  perfectly  colorless,  but  the  tints 
vary  through  all  the  shades,  and  some  diamonds  are  black.     Its 
density  is  about  3.5.     It  is  a  bad  conductor  of  heat  and  elec- 
tricity, and  strongly  refracts  light.     When  it  is  strongly  heated 
in  a  vacuum,  it  blackens,  and  is  converted  into  a  sort  of  coke. 
When  strongly  heated  in  oxygen,  it  burns  into  carbon  dioxide. 

224.  GRAPHITE,  or  plumbago,  is  often  called  black  lead.     It 


CARBON.  145 

occurs  in  brilliant  black  masses,  and  sometimes  in  six-sided  plates. 
It  is  soft  enough  to  be  easily  scratched  by  the  finger-nail,  and 
leaves  a  black  mark  on  paper.  Its  density  is  2.2,  and  it  is  a  good 
conductor  of  heat  and  electricity.  It  burns  into  carbon  dioxide 
when  heated  in  air  to  very  high  temperatures.  It  is  not  usually 
perfectly  pure  carbon,  but  contains  one  or  two  per  cent,  of  foreign 


FIG.  68. 

matters.  Graphite  is  used  in  lead-pencils,  and  for  the  manufac- 
ture of  crucibles :  in  the  latter  it  is  powdered  and  mixed  with 
clay,  which  binds  together  the  graphite.  It  is  employed  also  for 
coating  iron  objects  to  prevent  rusting,  and  as  a  lubricant  for 
machinery. 

225.  The  other  varieties  of  carbon  are  amorphous. 

ANTHRACITE  is  a  hard  and  brittle  substance,  containing  from 
8  to  10  per  cent,  of  earthy  matters,  and  sometimes  even  more. 

BITUMINOUS  COAL  is  softer  and  lighter  than  anthracite.  It 
contains  from  75  to  90  per  cent,  of  carbon,  with  which  is  com- 
bined a  varying  proportion  of  hydrogen.  It  is  the  remains  of 
vegetable  substances  which  were  buried  in  the  earth  in  the  early 
geological  ages.  When  it  is  strongly  heated  out  of  contact  with 
the  air,  various  compounds  of  hydrogen  and  carbon  are  formed, 
together  with  some  water  and  ammonia.  Certain  of  these  com- 
pounds of  carbon  and  hydrogen  are  gases,  and,  since  they  contain 
only  combustible  elements,  they  are  themselves  combustible. 

We  introduce  some  fragments  of  bituminous  coal  into  a  small 
glass  retort,  to  the  beak  of  which  we  have  adapted  a  little  jet 
(Fig.  69).  When  we  heat  the  retort  by  a  flame,  heavy  vapors  are 
disengaged  from  the  coal ;  some  of  them  condense  in  the  neck  of 

10 


146 


LESSONS    IN    CHEMISTRY. 


the  retort,  but  those  which  are  gaseous  at  ordinary  temperatures 
pass  out  at  the  jet,  and  when  we  apply  a  flame  they  burn  with  a 
bright  light.  This  is  precisely  the  operation  which  is  conducted 
for  the  manufacture  of  illuminating 
gas  from  bituminous  coal.  The  coal 
is  heated  in  clay  or  iron  retorts  (Fig. 
70),  and  the  liquid  products  are  con- 
densed by  passing  through  a  cold  pipe ; 
since  coal  always  contains  sulphur  and 
nitrogen,  some  hydrogen  sulphide  and 
ammonia  are  formed,  and  these  must  be 
separated  from  the  gas,  for  their  com- 
bustion would  render  the  air  of  a  room  quite  unwholesome.  They 
are  removed  by  passing  the  gas  through  a  tall,  upright  pipe  in 


A,  retorts.  B,  hydraulic  main  for 
condensation  of  liquid  products, 
C,  scrubbers,  in  which  gas  is  washed  with 
water-spray.  D,  lime-purifier.  E,  gas- 
holder. 


FIG.  70. 


which  little  jets  of  water  are  playing,  and  the  ammonia  and  hy- 
drogen sulphide  are  in  great  part  dissolved ;  the  gas  is  still  further 
purified  from  sulphur  by  passing  through  slaked  lime,  and  it  is  then 
conducted  into  large  gas-holders,  from  which  it  passes  into  the  pipes 


CARBON.  147 

for  consumption.  The  liquid  which  first  condenses  from  the  gas 
separates  into  two  layers ;  one  is  an  impure  solution  of  ammonia, 
and,  together  with  the  water  used  for  washing  the  gas,  forms  the 
source  of  the  ammonia  of  commerce  ;  the  other  is  tarry,  and  con- 
tains numerous  liquid  and  solid  compounds  of  carbon  and  hydrogen, 
which  we  must  study  at  another  time.  The  black  substance  which 
remains  in  the  clay  retorts,  as  it  does  in  our  glass  retort,  is  coke. 
As  some  of  the  compounds  of  hydrogen  and  carbon  which  are 
formed  are  decomposed  by  the  high  temperature  of  the  retorts, 
these  vessels  become  lined  with  the  carbon,  which  separates,  and 
forms  a  dense,  hard,  strong,  and  sonorous  layer.  It  is  called  gas 
carbon,  and  is  used  for  the  carbon  plates  of  voltaic  batteries  and 
for  the  carbon  electrodes  in  the  electric  light. 

The  minerals  lignite  and  jet,  of  which  ornaments  are  made,  are 
varieties  of  bituminous  coal. 

226.  CHARCOAL  is  derived  both  from  wood  and  from  animal 
matters.  Wood-charcoal  was  formerly  made  by  closely  piling  the 
wood  and  covering  the  pile  with  earth,  some  holes  being  left  for 
the  admission  of  air.  The  combustion  of  part  of  the  wood  then 
produces  sufficient  heat  to  convert  the  rest  into  charcoal,  or  car- 
bonize it.  This  process  is  very  wasteful :  not  only  is  a  large  quan- 
tity of  wood  unnecessarily  burned,  but  the  many  other  products, 
tar,  acetic  acid,  and  wood  alcohol,  which  might  be  obtained,  are 
lost.  Another  process  is  now  being  everywhere  adopted,  in  which 
the  wood  is  heated  in  iron  retorts,  and  the  vapors  given  off  are 
passed  through  pipes  surrounded  by  other  pipes  through  which 
flows  a  stream  of  cold  water ;  the  liquid  products  are  thus  con- 
densed, and  the  gases  are  conducted  under  the  retort  (Fig.  71). 
The  gas  from  one  retort  is  sufficient  to  carbonize  the  wood  in 
another,  so  that  after  starting  the  operation  little  or  no  fuel  is 
required  and  nothing  is  lost. 

Charcoal  is  brittle  and  sonorous ;  its  density  is  about  1.5.  It 
is  a  poor  conductor  of  heat  and  electricity.  It  is  not  pure  carbon : 
its  combustion  leaves  one  or  two  per  cent,  of  earthy  matter,  prin- 
cipally the  carbonates  of  potassium  and  calcium. 

ANIMAL  CHARCOAL  is  made  by  strongly  heating  waste  horn, 


148 


LESSONS   IN    CHEMISTRY. 


bone,  blood,  hide,  and  other  animal   matters,  in   closed  vessels. 
When  made  from  bone,  it  is  called  bone-black  or  ivory-black :  it 


FIG.  71. 

then  naturally  contains  the  mineral  matters  of  the  bones,  calcium 
phosphate  and  carbonate.  These  may  be  dissolved  out  by  wash- 
ing the  bone-black,  first 
with  hydrochloric  acid, 
and  afterwards  with 
water ;  it  is  then  called 
purified  animal  char- 
coal. 

LAMP-BLACK,  so 
much  used  for  the  manu- 
facture of  printing-ink, 
India-ink,  and  black 
paint,  is  made  by  burn- 
ing oil,  turpentine,  or 
rosin  in  an  insufficient 
supply  of  air.  The 
operation  is  conducted 
in  a  small  furnace  of 
which  the  chimney 
opens  into  a  room  on  whose  walls  the  thick  smoke  of  lamp-black 
settles.  Generally  these  walls  are  hung  with  canvas,  from  which 


FIG.  72. 


CARBON.  149 

the  lamp-black  is  removed  by  a  conical  scraper  which  can  be 
lowered  by  a  rope  passing  over  a  pulley  (Fig.  72).  Lamp-black 
is  a  fine  powder,  and  usually  contains  oily  and  tarry  matters  from 
the  rosin  :  it  may  be  purified  by  heating  it  red  hot  in  a  covered 
crucible. 

227.  Properties  of  Charcoal. — In  addition  to  the  peculiari- 
ties of  each  variety  which  we  have  considered,  all  of  the  forms  of 
charcoal  are  exceedingly  porous,  and  they  are  able  to  absorb  many 
times  their  volume  of  certain  gases.  We  fill  a  rather  wide  glass 
tube  with  mercury,  and,  after  inverting  it  in 
a  vessel  of  mercury,"  we  pass  into  it  some  am- 
monia gas,  made  by  boiling  a  little  ammonia- 
water  in  a  flask.  Now  we  heat  a  piece  of 
charcoal  red  hot,  to  drive  out  all  of  the  gases 
which  it  has  absorbed  from  the  air,  and  we 
push  it  under  the  mercury  into  the  tube 
(Fig.  73).  It  rises  to  the  surface,  and  in- 
stantly we  see  the  volume  of  ammonia  dimin- 
ishing; the  gas  is  being  absorbed  by  the 
charcoal,  and  after  we  remove  the  latter  from  ' 
the  tube  we  will  find  it  much  heavier,  and 
having  a  strong  odor  of  ammonia.  Charcoal 
will  absorb  about  ninety  times  its  volume  of  ammonia,  fifty-five  of 
hydrogen  sulphide,  and  large  quantities  of  most  other  gases.  It 
absorbs  less  than  twice  its  volume  of  hydrogen,  and  about  eight 
times  its  volume  of  either  carbon  monoxide,  oxygen,  or  nitrogen. 
These  gases  are  driven  out  when  the  charcoal  is  heated.  We  can 
now  understand  that  in  some  cases  charcoal  is  an  excellent  disin- 
fectant :  if  a  dead  mouse  or  other  small  animal  be  buried  in  a  box 
of  powdered  charcoal,  it  will  be  found  after  some  weeks  to  have 
dried  up,  and  the  charcoal  will  have  absorbed  all  of  the  unpleasant 
odors.  Charcoal  has  also  the  property  of  absorbing  many  color- 
ing matters  in  its  pores,  where  they  are  probably  oxidized  :  animal 
charcoal  possesses  this  property  in  the  most  marked  degree.  We 
pour  some  litmus  solution  into  a  filter  containing  animal  charcoal, 
and  the  liquid  passes  through  colorless.  This  peculiarity  renders 


150  LESSONS    IN    CHEMISTRY. 

animal  charcoal  valuable  for  decolorizing  many  liquids,  and  enor- 
mous quantities  of  it  are  employed  for  decolorizing  sugar.  The 
brown  color  is  removed  from  crude  sugar  by  dissolving  it  in  water 
and  filtering  the  syrup  through  animal  charcoal.  An  excellent 
filter  for  the  purification  of  drinking-water  consists  of  a  layer  of 
charcoal  between  two  layers  of  sand  :  the  charcoal  must  be  changed 
from  time  to  time,  or  it  may  be  removed  and  heated  red  hot  in  a 
covered  vessel ;  it  is  then  again  fit  for  use. 

228.  The  strongest  affinity  of  carbon  is  for  oxygen,  but  this 
affinity  is  not  manifested  at  ordinary  temperatures.  When,  how- 
ever, the  temperature  is  raised  to  redness  and  the  combustion  of 
charcoal  begins,  sufficient  energy  is  developed  by  the  chemical 
action  to  keep  the  temperature  at  the  combining  point,  and  the 
oxidation  goes  on  without  further  aid.  The  product  of  the  com- 
bustion of  carbon  in  air  or  in  oxygen  is  carbon  dioxide,  CO2.  Be- 
cause of  its  strong  affinity  for  oxygen,  charcoal  can  remove  that 
element  from  various  oxidized  bodies  :  it  is  a  reducing  agent.  We 
have  already  seen  an  example  of  this  reduction  when  we  heated 
charcoal  with  cupric  oxide  (§  13).  When  such  a  reduction  re- 
quires a  temperature  about  redness,  carbon  dioxide  is  formed,  and 
this  was  the  case  with  cupric  oxide  and  charcoal. 

2CuO        +        C        =        Cu2        +        CO2 
Cupric  oxide.  Copper.         Carbon  dioxide. 

When,  however,  the  reduction  requires  a  white  heat,  or  near 
that  temperature,  carbon  monoxide,  CO,  is  formed.  This  is  the 
action  of  charcoal  on  zinc  oxide. 

ZnO        +        C        =  CO  +        Zn 

Zinc  oxide.  Carbon  monoxide. 


LESSON    XXIX. 
OXIDES   OP  CARBON. 

229.  Carbon  Monoxide,  CO. — This  gas  might  be  made  by 
heating  to  whiteness  in  clay  retorts  a  mixture  of  zinc  oxide  and 
charcoal,  but  this  would  require  a  furnace  and  be  inconvenient. 


CARBON    MONOXIDE. 


151 


We  can  prepare  the  gas  more  conveniently  by  heating  in  a  glass 
flask  a  mixture  of  oxalic  and  strong  sulphuric  acids.  The  oxalic 
acid,  which  is  a  compound  of  carbon,  oxygen,  and  hydrogen,  is 
then  decomposed  into  carbon  monoxide,  carbon  dioxide,  and  water. 


C204H2 

Oxalic  acid. 


CO2  +  CO  + 

Carbon  dioxide.        Carbon  monoxide. 


The  water  will  be  retained  by  the  sulphuric  acid,  but  we  must  pass 
the  gases  through  a  bottle  containing  a  solution  of  sodium  hydrox- 
ide, by  which  the  carbon  dioxide  will  be  absorbed.  Sodium  car- 
bonate is  formed  in  the  bottle,  and  we  collect  the  carbon  monoxide 
over  water  (Fig.  74). 


FIG.  74. 

230.  Carbon  monoxide  is  a  colorless,  odorless  gas.  Its  density 
compared  to  air  is  0.967,  or  compared  to  hydrogen,  14.  It  is  in- 
soluble in  water.  It  is  very  poisonous  :  when  it  is  taken  into  the 
lungs  it  combines  with  the  red  globules  in  the  blood,  and  prevents 
them  from  carrying  into  the  system  the  oxygen  which  is  necessary 
for  the  processes  of  life  (§  33). 


152  LESSONS    IN    CHEMISTRY. 

Just  as  we  made  a  similar  experiment  with  hydrogen,  carefully 
we  lift  our  jar  from  the  water,  and  push  into  it  a  lighted  tape.'. 
The  gas  takes  fire  and  burns  with  a  blue  flame  at  the  mouth  of 
the  jar,  but  the  taper  is  extinguished.  Carbon  monoxide  will  not 
support  combustion,  but  it  will  combine  with  oxygen  to  form  carbon 
dioxide. 

It  is  interesting  here  to  study  the  amount  of  heat  disengaged  by  the  com- 
bustion of  carbon.  Naturally,  we  can  understand  that  when  a  given  weight 
of  charcoal  is  burned,  a  fixed  quantity  of  heat  will  be  developed,  enough  to 
raise  a  certain  weight  of  water,  let  us  say,  from  0°  to  1°.  When  this  same 
weight  of  charcoal  is  converted  into  carbon  monoxide,  the  combustion  of  the 
latter  gas  will  not  heat  as  much  water  through  the  same  temperature.  What 
has  become  of  the  energy  which  has  disappeared  from  the  charcoal  ?  It  must 
have  been  lost  from  the  atom  of  carbon  and  the  first  atom  of  oxygen  with 
which  it  combined.  Many  careful  experiments  have  shown  that  this  is  the 
case,  and  that  the  same  quantity  of  carbon  always  develops  the  same  quan- 
tity of  heat  when  it  is  converted  into  carbon  dioxide,  whether  it  is  so  con- 
verted at  once,  or  whether  it  first  forms  carbon  monoxide  and  this  combines 
with  an  additional  atom  of  oxygen.  We  so  have  a  method  which  enables  us 
to  determine  the  heat  or  energy  of  formation  of  bodies  like  carbon  monoxide. 
For  if  from  the  amount  of  energy  developed  by  the  conversion  of  a  certain 
amount  of  carbon  into  carbon  dioxide,  we  subtract  that  which  is  developed  by 
the  combustion  of  a  quantity  of  carbon  monoxide  containing  the  same  weight 
uf  carbon,  we  will  have  the  energy  with  which  one  atom  of  carbon  combines 
with  one  atom  of  oxygen.  In  making  such  determinations,  a  number  of 
grammes  of  the  substance  is  taken  which  would  express  the  atomic  weight  if 
one  atom  of  hydrogen  weighed  one  gramme ;  and  the  result,  which  is  expressed 
in  the  number  of  kilogrammes  of  water  which  would  be  raised  from  0°  to  1° 
oy  the  heat  produced,  is  called  the  heat  of  formation  of  the  compound. 

231.  Carbon  monoxide  is  formed  by  the  action  of  carbon  dioxide 
on  carbon  at  very  high  temperatures. 

CO2    +    C    =    2CO 

When  fresh  coal  is  thrown  on  a  hot  fire,  the  escape  of  the  carbon 
dioxide  from  the  burning  coal  is  retarded,  and  that  gas  remains 
in  contact  with  the  coal  long  enough  to  be  partially  reduced  to 
carbon  monoxide.  The  latter  then  occasions  the  blue  flame  with 
which  we  are  all  familiar.  Carbon  monoxide  has  the  property  of 
passing  through  the  pores  of  red-hot  iron,  and  it  often  so  escapes 
through  the  iron  of  stoves  which  are  not  properly  lined  with  fire- 
brick ;  fortunately,  the  gas  formed  from  coal  has  a  decided  odor, 


CARBON   DIOXIDE.  153 

usually  due  to  the  sulphur  in  the  coal,  and  this  odor  generally 
makes  us  aware  of  the  presence  of  the  poisonous  gas. 

232.  When  steam  is  passed  over  hot  coal  or  charcoal,  a  mixture 
of  carbon  monoxide  and  hydrogen  is  formed. 
C    +    H20    =    CO    +    H2 

When  this  mixture  is  passed  through  volatile  compounds  of 
hydrogen  and  carbon,  such  as  we  shall  learn  are  contained  in  the 
lighter  kinds  of  petroleum,  the  gases  become  charged  with  the 
vapors  of  those  compounds :  if  they  then  be  passed  through  hot 
pipes,  various  gaseous  compounds  of  carbon  and  hydrogen  are 
formed,  and  these  burn  with  light-giving  flames.  The  water-gas 
used  for  illumination  in  some  cities  is  manufactured  in  this  manner. 

233.  CARBONYL  CHLORIDE. — Carbon  monoxide  combines  directly  with  chlo- 
rine when  a  mixture  of  the  two  gases  is  exposed  to  direct  sunlight,  and  a 
suffocating  gas,  phosgene  or  carbonyl  chloride,  COC12,  is  formed.  The  carbon 
monoxide  acts  as  a  radical,  which  is  called  carbonyl.  Carbonyl  chloride  reacts 
with  water,  and  yields  carbon  dioxide  and  hydrochloric  acid. 

COC12     +     H20    =     CO2     +     2HC1 

Carbon  monoxide  also  unites  directly  with  certain  metals.  When  it  is  passed 
over  finely  divided  nickel,  there  results  nickel  carbonyl,  Ni(CO)4,  a  volatile, 
highly-refracting  liquid.  Its  vapor  is  very  poisonous,  and  it  burns  with  a 
luminous  flame.  A  similar  iron  compound,  Fe(CO)5,  is  also  known. 

234.  Carbon  Dioxide,  CO2. — In  a  gas-bottle,  like  that  which 
we  used  for  preparing  hydrogen  (Fig.  75),  we  put  some  water  and 

broken  marble,  and  pour  hydro- 
chloric acid  through  the  funnel- 
tube.  As  the  gas  with  which 
we  wish  to  experiment  is  very 
heavy,  we  collect  it  by  down- 
ward dry  displacement,  passing 
the  end  of  our  delivery-tube  to 
the  bottom  of  the  jar.  When 
the  effervescence  in  the  bottle 
has  continued  for  a  moment, 
we  put  a  lighted  taper  into  the 
_,  --  jar  in  which  we  are  collecting 

the  gas :  the  flame  is  at  once 
extinguished.     The  jar  is  full  of  carbon  dioxide,  and  for  such 


154  LESSONS    IN    CHEMISTRY. 

substances  as  the  matter  of  the  taper  the  oxygen  in  this  gas 
has  exhausted  its  energy  in  combining  with  the  carbon :  it  will 
unite  with  no  more.  In  our  gas-bottle  we  have  formed  water  and 
calcium  chloride,  for  marble  is  calcium  carbonate. 

CaCO3      +        2HC1        =        CaCl2         +       H20      +      CO2 
Calcium  carbonate.  Calcium  chloride. 

235.  Carbon  dioxide  is  a  colorless  gas  ;  it  has  a  faint  but  some- 
what pungent  odor  and  taste.      Its  density  compared  to  air  is 
1.529,  or  compared  to  hydrogen,  22.     We  balance  on  a  scale-pan 
an  open  and  erect  paper  bag,  into  which  we  quickly  pour  the  car- 
bon dioxide  from  our  jar  :  the  descending  pan  at  once  shows  us 
that  the  gas  is  heavier  than  the  air  which  it  displaces.     At  0°,  it 
is  converted  into  a  colorless  liquid  by  a  pressure  of  thirty-six  at- 
mospheres, and  when  the  liquid  is  allowed  to  evaporate  rapidly, 
it  absorbs  so  much  heat  in  assuming  the  gaseous  state  that  the 
temperature  falls  to  — 78°,  and  a  part  of  the  carbon  dioxide  is 
frozen  to  a  snow-like  mass.     When  touched,  this  solid  produces  a 
burn  like  fire,  for  the  life  of  animal  tissues  cannot  continue  at 
such  low  temperatures. 

Carbon  dioxide  is  soluble  in  its  own  volume  of  water,  and  the 
quantity  of  the  gas  which  can  be  absorbed  by  a  given  quantity  of 
water  is  directly  proportional  to  the  pressure :  if  the  pressure  be 
doubled,  twice  as  much  gas  will  be  dissolved,  etc.  We  know, 
however,  that  by  a  double  pressure  two  volumes  of  any  gas  will 
be  reduced  to  one  volume  (Mariotte's  law)  :  hence  we  may  say 
that  water  always  dissolves  its  own  volume  of  carbon  dioxide,  no 
matter  what  the  pressure.  When  the  pressure  is  diminished  or 
removed,  the  gas  escapes  with  effervescence,  until  the  volume 
remaining  dissolved  is  equal  to  that  of  the  water.  The  beverage 
generally  known  as  aerated  water  or  soda-water,  is  simply  water 
into  which  about  five  times  its  volume  of  carbon  dioxide  has  been 
pumped. 

236.  We  have  already  seen  that  carbon  dioxide  neither  burns 
nor  supports  combustion,  and  a  simple  experiment  shows  us  its 
power  of  extinguishing  burning  bodies,  at  the  same  time  that  we 
will  be  reminded  of  its  weight.     We  fix  a  short  taper  or  piece  of 
candle  in  a  cork,  and,  after  lighting  it,  put  it  in  a  small  jar  into 


CARBON    DIOXIDE. 


155 


which  we  pour  the  carbon  dioxide  from  another  jar  which  we  have 
filled  by  dry  displacement :  the  flame  is  extinguished  as  if  we  had 
poured  water  on  it  (Fig.  76).  Carbon 
dioxide  is  not  poisonous,  but  it  pro- 
duces death  by  suffocation, — that  is, 
exclusion  of  oxygen.  It  collects  in 
wells  and  brewers'  vats,  and  may  then 
be  detected  by  its  power  of  extinguish- 
ing flames  lowered  into  it :  if  there  be 
enough  of  the  gas  present  to  extin- 
guish or  nearly  extinguish  a  flame, 
it  would  not  be  safe  for  a  man  to  enter 
such  a  place  before  removing  the  gas, 
which  can  be  done  by  agitating  the 
air  so  that  currents  maybe  established. 

237.  Certain  substances  which  have  the  power  of  reducing 
carbon  dioxide  may  burn  in  the  gas.  Over  a  piece  of  the  metal 
potassium  contained  in  a  glass  bulb,  we  pass  carbon  dioxide  that 

O 


FIG.  77. 


has  been  dried  by  passing  through  a  tube  containing  pumice-stone 
and  sulphuric  acid.  When  we  warm  the  potassium,  it  takes  fire 
and  burns  with  a  red  light,  and  a  deposit  of  carbon  is  formed 
in  the  bulb  (Fig.  77).  The  potassium  has  reduced  some  of  the 


156  LESSONS    IN    CHEMISTRY. 

carbon  dioxide,  and  has  combined  with  another  portion,  forming 
potassium  carbonate. 

238.  We  pass  a  few  bubbles  of  carbon  dioxide  into  some  lime- 
water  :  the  liquid  quickly  becomes  milky  by  the  formation  of  in- 
soluble calcium  carbonate.  This  test  enables  us  to  recognize  carbon 
dioxide.  Calcium  carbonate  is  insoluble  in  water,  but  if  we  pass 
the  gas  for  a  long  time  through  our  milky  liquid,  the  cloudiness 
disappears ;  water  containing  carbon  dioxide  in  solution  will  dis- 
solve calcium  carbonate.  If,  however,  we  boil  this  liquid  so  that 
all  of  the  dissolved  carbon  dioxide  shall  be  driven  out,  the  calcium 
carbonate  again  separates,  usually  as  small  crystalline  particles, 
which  settle  as  the  water  cools.  The  stalactites  and  incrustations 
in  caves  are  formed  by  the  drippings  of  water  holding  calcium 
carbonate  in  solution  by  an  excess  of  carbon  dioxide ;  as  the  gas 
passes  off  gradually  into  the  air,  the  calcium  carbonate  becomes 
insoluble  and  is  deposited. 


LESSON    XXX. 

CARBONATES. 

239.  Carbon  dioxide  corresponds  to  an  acid  which  would  be  formed  by  the 
action  of  one  molecule  of  the  gas  on  one  molecule  of  water.  The  solution  of 
the  gas  in  water  is  feebly  acid,  and  we  may  believe  that  it  contains  carbonic 
acid,  H2C03  =  CO2  f  H20.  Carbon  dioxide  is  often  called  carbonic  anhydride ; 
anhydride  means  without  water,  and  carbonic  anhydride  thus  signifies  carbonic 
acid  less  the  elements  of  water.  Although  this  acid  cannot  be  separated  from 
the  solution,  for  when  the  water  is  evaporated  carbon  dioxide  is  driven  out, 
there  are  numerous  salts  formed  by  the  replacement  of  one  or  both  of  the 
atoms  of  hydrogen  in  H2C03.  These  salts  are  the  carbonates ;  they  may  be 
easily  recognized  by  the  action  of  hydrochloric  acid,  which  produces  with 
them  an  effervescence  due  to  the  escape  of  carbon  dioxide ;  we  may  identify 
this  gas  by  the  milkiness  which  it  produces  in  lime-water. 

There  are  two  classes  of  carbonates ;  those  in  which  both  atoms  of  hydrogen 
in  H2C03  are  replaced  by  metal,  and  others  in  which  only  one  of  these  atoms 
is  replaced.  The  latter  are  called  the  acid  carbonates,  or  sometimes  the  dicar- 
bonates.  Carbonic  acid  is,  then,  dibasic. 


SODIUM    CARBONATE.  157 

With  the  exception  of  the  carbonates  of  sodium,  potassium,  and 
lithium,  all  of  the  carbonates  of  the  metals  are  insoluble  in  water : 
they  dissolve  slightly,  however,  in  water  containing  carbon  dioxide. 
They  all  effervesce  when  treated  with  hydrochloric  or  sulphuric 
acid,  carbon  dioxide  being  disengaged. 

240.  Sodium  Carbonate,  Na2C03. — Enormous  quantities  of 
this  salt,  which  is  commonly  called  soda,  or  sal  soda,  are  used  for 
the  manufacture  of  glass  and  of  soap,  and  for  the  preparation  of 
the  many  compounds  of  sodium  that  are  used  in  the  arts.  It  is 
usually  manufactured  from  common  salt,  and  the  process  which  is 
coming  into  general  use  depends  on  a  reaction  between  the  salt 
and  ammonium  acid  carbonate  (§  251).  We  mix  saturated  solu- 
tions of  ammonium  acid  carbonate  and  sodium  chloride,  and  a  fine 
white  deposit  is  formed  in  the  liquid.  This  is  sodium  acid  car- 
bonate, and  ammonium  chloride  exists  in  the  solution. 

NaCl        +        (NH*)HC03        =          NH*C1  +        NaTICO3 

Sodium  chloride.  Ammonium  acid  Ammonium  chloride.  Sodium  acid 

carbonate.  carbonate. 

This  operation  is  conducted  on  a  large  scale,  and  the  sodium 
acid  carbonate  is  converted  into  sodium  carbonate  by  the  action  of 
heat.  Two  molecules  of  the  acid  carbonate  then  lose  one  molecule 
of  water,  and  one  of  carbon  dioxide. 

2NaHC03  =  Na2C03  +         H20         +         CO2 

Sodium  acid  carbonate.  Sodium  carbonate. 

The  ammonium  chloride  is  converted  into  ammonia  by  heating 
it  with  lime  (§  136),  and  the  carbon  dioxide  formed  by  heating  the 
sodium  acid  carbonate,  together  with  more  which  is  obtained  from 
the  gases  of  the  furnace-chimneys,  serves  to  convert  the  ammonia 
again  into  ammonium  acid  carbonate. 

Nil3    +     H20     +    CO2    =    (NH4)HC03 

The  only  waste  product  is,  then,  the  calcium  chloride  left  after 
the  preparation  of  the  ammonia.  In  the  older  process,  which  the 
ammonia-soda  process  is  gradually  replacing,  the  sodium  chloride 
is  first  converted  into  sodium  sulphate  (§  77) ;  this  is  mixed  with 
chalk  and  coal,  and  the  mixture  heated  by  the  flame  of  a  rever- 
beratory  furnace  (Fig.  78)  yields  a  mixture  containing  calcium 
sulphide  and  sodium  carbonate.  The  last  is  dissolved  out  by  water, 


158 


LESSONS   IN    CHEMISTRY. 


and  the  waste  heat  of  the  furnace  is  employed  not  only  to  evar> 
orate  the  solution  obtained  (C  and  D),  but  to  dry  the  mixture  of 
sodium  sulphate,  chalk,  and  coal  (B)  before  introducing  it  into 
the  hottest  part  of  the  furnace  (A).  This  is  named,  from  its 
inventor,  the  Leblanc  process. 

Sodium  carbonate  is  also  manufactured  from  the  mineral  cryolite, 
a  double  fluoride  of  sodium  and  aluminium,  of  which  large  quan- 


FIG.  78. 

tities  are  found  in  Greenland.  The  cryolite  is  heated  with  lime, 
and  the  reaction  yields  calcium  fluoride  and  a  compound  known  as 
aluminate  of  sodium :  it  is  a  combination  of  the  oxides  of  sodium 
and  aluminium. 

2AlF3.3NaF      +     6CaO     =         6CaF2          +          Al203.3Na20 
Cryolite.  Lime.          Calcium  fluoride.        Aluminate  of  sodium. 

The  aluminate  of  sodium  is  dissolved  from  the  mass  by  water,  and 
carbon  dioxide  passed  through  the  solution  forms  sodium  carbonate, 
while  insoluble  aluminium  hydroxide  is  precipitated. 

Al203.3Na20       +     3C02     +     3H20     =        2A1(OH)3  +     3Na2C03 

Aluminate  of  sodium.  Aluminium  hydroxide. 

The  aluminium  hydroxide  is  used  for  the  manufacture  of  alum. 

Sodium  carbonate  forms  large  crystals  containing  ten  molecules 
of  water  of  crystallization  for  one  molecule  of  the  salt.  When  it 
is  exposed  to  the  air,  it  gradually  loses  this  water,  and  falls  to  a 
dry,  white  powder :  it  is  said  to  effloresce.  The  crystals  dissolve 
in  about  four  times  their  weight  of  water  at  20°,  and  the  solution 
has  an  alkaline  reaction  and  an  unpleasant  alkaline  taste-  The 
salt  is  insoluble  in  alcohol. 

241.  Sodium  Acid  Carbonate,  NaHCO3,  is  less  soluble  than 


POTASSIUM    CARBONATE.  159 

the  carbonate,  and  is  precipitated  when  carbon  dioxide  is  passed 
through  a  saturated  solution  of  the  latter  salt.  It  is  usually  a 
white  powder,  which,  when  heated  or  boiled  with  water,  is  decom- 
posed into  water,  sodium  carbonate,  and  carbon  dioxide  which 
escapes.  It  is  commonly  called  bicarbonate  of  soda,  or  baking- 
soda;  it  forms  part  of  the  mixtures  known  as  baking-powders, 
which  contain  some  acid  substance  that  may  react  with  the  acid 
carbonate,  setting  free  carbon  dioxide  in  bubbles  through  the 
dough.  Sodium  acid  phosphate  is  such  a  substance ;  sodium  acid 
carbonate  may  convert  it  into  either  disodium  or  trisodium  phos- 
phate. 

NaHCO3     +     NaH2FO*    =»     Na'HPO4     +     H'O     +     CQ2 

242.  Potassium  Carbonate,  K2C03. — This  compound  is  com- 
monly called  potash,  because  it  was  for  a  long  time  derived  only 
from  wood-ashes ;  it  is  extracted  from  the  ashes  by  causing  water 
to  trickle  through  them,  a  process  which  is  called  lixiviation.  The 
solution  so  obtained  is  evaporated  to  dryness,  and  the  residue 
strongly  heated  in  the  air.  The  potash  of  commerce  contains  only 
from  60  to  80  per  cent,  of  potassium  carbonate.  The  remainder 
consists  of  other  potassium  salts,  principally  the  chloride  and  sul- 
phate :  when  these  are  partially  removed  by  an  imperfect  purifica- 
tion, the  product  is  called  pearl-ash. 

At  Stassfurt,  in  Prussia,  there  are  large  deposits  of  a  double 
chloride  of  potassium  and  magnesium  ;  the  mineral  is  called 
carnattite,  and  contains  KCl.MgCl*  -f-  6H20.  It  is  decomposed 
by  boiling  with  water,  and,  on  cooling,  potassium  chloride  crys- 
tallizes from  the  liquid,  while  magnesium  chloride  remains  in 
the  solution.  Potassium  carbonate  is  now  manufactured  from 
this  potassium  chloride  by  a  method  similar  to  the  Leblanc 
process  for  sodium  carbonate. 

Potassium  carbonate  is  white,  and  dissolves  in  less  than  its  own 
weight  of  water.  It  is  very  alkaline,  and  has  a  burning  taste. 
It  is  deliquescent ;  that  is,  it  attracts  moisture  from  the  air  and 
dissolves  in  the  water  so  absorbed.  It  may  be  obtained  in  crys- 
tals containing  two  molecules  of  water  by  allowing  a  hot  concen- 
trated solution  to  cool. 


160  LESSONS   IN   CHEMISTRY. 

243.  Potassium  Acid  Carbonate,  KHCO3,  is  prepared,  like 
bicarbonate  of  soda,  by  passing  carbon  dioxide  through  a  solu- 
tion of  the  neutral  carbonate.     It  is  less  soluble  than  the  latter, 
and  separates  from  the  solution  in  crystals.     Like  sodium  acid 
carbonate,  it  is  decomposed  by  heat,  whether  it  be  dry  or  in 
solution. 

244.  Calcium  Carbonate,  CaCO3. — This  substance  is  one  of 
the  most  abundant  of  minerals.     As  calcite,  or  Iceland  spar,  it 
forms  doubly-refracting  rhombohedra :  as  aragonite,  it  occurs 
in  rhombic  prisms.     It  also  constitutes  marble,  limestone,  chalk, 
and  the  greater  part  of  the  matter  of  shells  and  corals.     When 
heated  to  bright  redness  in  open  vessels,  it  is  decomposed  into 
carbon  dioxide  and  lime,  which  is  calcium  oxide. 

245.  Strontium  Carbonate,   SrCO3,   constitutes    the    white 
mineral  strontianite. 

246.  Barium  Carbonate,  BaCO3,  is  found  crystallized  in  nature 
in  the  mineral  witherite.     The  carbonates  of  calcium,  strontium, 
and  barium  are  precipitated  when  a  solution  of  sodium  or  potas- 
sium carbonate  is  added  to  a  neutral  solution  of  any  calcium, 
strontium,  or  barium  salt. 

24*7.  Magnesium  Carbonate,  MgCO*,  constitutes  the  minerals 
magnesite  and  giobertite.  Dolomite  is  a  double  carbonate  of  calcium 
and  magnesium  ;  it  is  a  magnesian  limestone.  White  magnesia  is 
a  variable  compound  of  magnesium  carbonate  and  magnesium 
hydrate,  made  by  adding  an  excess  of  sodium  carbonate  solution 
to  a  boiling  solution  of  magnesium  sulphate,  and  drying  the  pre- 
cipitate. 

248.  Zinc  Carbonate,  ZuCO3,  constitutes  the  mineral  smith 
sonite,  an  important  ore  of  zinc. 

249.  Ferrous  Carbonate,   FeCO3,  is  found  native  in  brown 
crystals  as  siderite  or  spathic  iron. 

250.  Lead  Carbonate,  PbCO3,  is  met  with  as  cerussite.     It 
is  precipitated  as  an  amorphous  white  powder  when  any  soluble 
lead  salt  is  treated  with  sodium  carbonate.      White  lead  is  a  mix- 
ture of  varying  proportions  of  lead  carbonate  and  lead  hydroxide. 
It  is  manufactured  by  the  joint  action  of  carbon  dioxide  and 


AMMONIUM    CARBONATES.  161 

Vapor  of  acetic  acid  on  metallic  lead.  Acetic  acid,  that  is,  vinegar, 
is  put  into  earthen  pots,  and  the  lead,  either  in  a  rolled  sheet  or 
in  flat  rings,  is  supported  on  little  pro- 
jections above  the  vinegar  (Fig.  79). 
A  great  number  of  these  pots  are  pre- 
pared, and  loosely  covered  with  disks 
of  lead  (D)  :  they  are  then  arranged  in 
layers  on  boards,  each  layer  resting  on 
a  bed  of  refuse  bark  from  tanneries,  or 
of  horse-manure.  These  substances  un- 
dergo a  sort  of  slow  oxidation,  and  dis- 
engage carbon  dioxide,  which  in  the 

presence  of  the  acetic  acid  converts  the  surface  of  the  lead  into 
carbonate.  We  may  suppose  that  lead  acetate  is  first  formed,  and 
that  this  is  at  once  decomposed  by  the  carbon  dioxide,  forming 
lead  carbonate,  while  acetic  acid  is  regenerated.  When  the  greater 
part  of  the  lead  has  been  so  changed  into  carbonate,  the  pots  are 
opened  and  the  white  lead  is  scraped  from  the  remaining  metal. 

There  is  another  process,  which  depends  on  the  facility  with 
which  lead  acetate  solution  dissolves  lead  oxide,  and  with  which 
this  oxide  is  precipitated  as  carbonate  when  carbon  dioxide  is  passed 
through  the  solution.  Lead  acetate  is  then  again  formed  in  the 
solution,  and  is  used  to  dissolve  more  oxide,  which  is  in  its  turn 
precipitated  by  carbon  dioxide. 

Excepting  sodium  carbonate  and  potassium  carbonate,  all  the 
other  salts  which  we  have  just  considered  are  decomposed  by  heat 
into  carbon  dioxide  and  oxide  of  the  metal. 

251.  Ammonium  Carbonates. — The  ammonium  carbonate  of 
commerce  is  commonly  called  a  sesquicarbonate,  and  is  probably 
a  mixture  of  several  bodies.  It  is  made  by  subliming  a  mixture 
of  chalk  and  ammonium  sulphate  in  large  retorts.  Its  compo- 
sition is  expressed  by  the  formula  2[(NH*)2C03]  +  CO2  -f-  H20. 
It  is  a  crystalline  substance,  having  a  strong  ammoniacal  odor 
and  a  sharp,  burning  taste.  It  is  soluble  in  water.  When  it  is 
exposed  to  the  air,  it  gradually  decomposes,  losing  ammonia  and 
leaving  ammonium  acid  carbonate,  NHMICO3.  The  latter  body 

11 


162  LESSONS    IN    CHEMISTRY. 

may  also  be  formed  by  passing  carbon  dioxide  into  ammonia- water 
until  no  more  of  the  gas  is  absorbed.  It  tben  crystallizes  when 
the  liquid  is  cooled.  Ammonium  carbonate,  (NH4)2C03,  separates 
in  crystals  when  the  ammonium  carbonate  of  commerce  is  dis- 
solved in  ammonia-water  and  the  solution  is  artificially  cooled. 


LESSON    XXXI. 

COMPOUNDS   OP  CARBON  WITH   SULPHUR  AND 
NITROGEN. 

252.  Carbon  Bisulphide,  CS2. — When  sulphur  vapor  is  passed 
over  red  hot  charcoal  or  coal,  the  two  elements  combine,  forming 
carbon  disulphide,  which  passes  off  as  a  vapor  that  may  be  con- 
densed in  any  suitable  cooling  apparatus.  This  substance  is 
manufactured  by  throwing  sulphur  into  coal  heated  to  redness  in 
inclined  iron  cylinders,  provided  with  openings  for  the  introduction 
of  sulphur  and  the  escape  of  the  vapor. 

It  is  a  colorless  liquid,  having  the  property  of  highly  refracting 
light.  When  pure,  it  has  a  rather  pleasant  odor,  but  the  com- 
mercial product  usually  contains  small  quantities  of  other  com- 
pounds which  communicate  to  the  liquid  a  strong  and  often  dis- 
gusting odor :  it  is  purified  by  distillation  with  lime.  Its  density 
at  15°  is  1.27.  .  It  is  almost  insoluble  in  water.  It  boils  at  46°. 
It  is  very  inflammable :  we  heat  a  wire  to  redness,  withdraw  it 
from  the  flame,  and  for  some  time  after  it  has  cooled  below  a 
visible  heat  it  will  still  inflame  carbon  disulphide  contained  in  a 
small  dish.  The  vapor  forms  an  explosive  mixture  with  the  air 
or  with  oxygen.  The  products  of  the  combustion  of  carbon  di- 
sulphide are  carbon  dioxide  and  sulphur  dioxide. 
CS2  +.  302  =  CO2  +  2S02 

If  a  few  thin  iron  wires  are  held  in  the  flame  of  vapor  of  carbon 
disulphide  which  is  heated  in  a  small  test-tube  provided  with  a 
cork  and  jet,  the  air  and  sulphur  combine,  producing  brilliant 


CARBON   BISULPHIDE. 


163 


sparks  and  molten  globules  of  iron  sulphide,  which  drop  from  the 
ends  of  the  wires  (Fig.  80). 
.  Carbon  disulphide  is  used 
for  extracting  oil  from  seeds 
and  other  matters,  for  it 
dissolves  fatty  substances 
quickly  and  in  the  cold, 
and  may  readily  be  distilled 
and  recovered  from  the  so- 
lution, leaving  a  much  larger 
quantity  of  oil  than  could 
be  extracted  by  pressure. 
It  is  used  in  vulcanizing 
caoutchouc,  an  operation 
which  depends  on  the  com- 
bination of  the  caoutchouc  FIG.  80. 
with  a  certain  quantity  of 

sulphur,  as  it  is  able  to  dissolve  not  only  the  caoutchouc  but  the 
sulphur  chloride  which  is  used  in  the  operation.  We  have  seen 
that  carbon  disulphide  dissolves  iodine,  sulphur,  and  phosphorus. 
253.  Carbon  disulphide  is  closely  related  to  carbon  dioxide. 
We  have  studied  the  general  composition  of  the  carbonates,  and 
know  that  they  correspond  to  a  carbonic  acid  which  should  con- 
tain H2C03.  There  is  also  a  series  of  thiocarbonates  or  sulpho- 
carbonates,  exactly  similar  to  the  carbonates  in  composition,  but 
they  contain  three  sulphur  atoms  instead  of  three  atoms  of  oxygen. 

(H'CO3)  Carbonic  acid.  H'CS3,    Thiocarbonic  acid. 

Na2C03,  Sodium  carbonate.  Na'CS3,  Sodium  thiocarbonate. 

KaC03,     Potassium  carbonate.          KaCS3,     Potassium  thiocarbonate. 
The   thiocarbonates   as   well   as   carbon    disulphide   are   em- 
ployed to  destroy  vermin,  a  purpose  for  which  they  are  quite 
effective. 

254.  If  we  compare  together  the  molecules  of  the  few  compounds  of  carbon 
which  we  have  studied,  we  will  find  that  in  all  excepting  one  an  atom  of  car- 
bon has  as  much  combining  power  as  four  atoms  of  hydrogen.  It  is  tetra- 
tomic :  in  carbon  dioxide,  because  it  is  united  with  two  atoms  of  oxygen,  each 
of  which  is  worth  two  atoms  of  hydrogen  ;  in  sodium  carbonate,  for  it  is  there 
combined  with  one  atom  of  oxygen  and  two  other  atoms  of  oxygen,  each  of  which 
brings  into  the  system  a  sodium  atom  as  a  satellite;  in  carbon  disulphide, 


164 


LESSONS    IN   CHEMISTRY. 


C=0  C1-C-C1 

1 1 
0 

Carbon  Carbonyl 

monoxide.         chloride. 


o=c=o 

Carbon 
dioxide. 


S=OS         0=C=S 

Carbon          Carbon 
disulphide.  oxysulphide. 


where  it  is  combined  with  two  atoms  of  diatomic  sulphur ;  and  there  is  also 
a  carbon  oxysulphide,  COS,  in  which  one  atom  of  oxygen  and  one  of  diatomic 
sulphur  satisfy  the  combining  capacity  of  the  tetratomic  carbon  atom.  How- 
ever, in  carbon  monoxide  either  the  carbon  atom  must  be  diatomic, — that  is, 
worth  two  atoms  of  hydrogen, — or  the  oxygen  atom  must  be  tetratomic.  Since 
we  know  that  carbon  monoxide  can  combine  with  two  atoms  of  chlorine,  each 
of  which  has  the  power  of  one  hydrogen  atom,  and  that  it  may  also  combine 
with  another  oxygen  atom,  we  must  consider  that  the  carbon  atom  is  diatomic 
in  a  molecule  of  carbon  monoxide,  which  is  then  an  unsaturated  compound. 
We  may  represent  the  structure  of  these  molecules,  as  we  have  expressed  that 
of  others,  by  structural  formulae  : 

NaO-C-ONa 

0 

Sodium 
carbonate. 

After  a  time  we  shall  become  acquainted  with  compounds  in  which  the 
group  CS  acts  as  a  radical,  precisely  as  does  the  group  carbonyl,  CO ;  so  that 
we  may  consider  the  compound  COS  either  as  a  combination  of  carbonyl  with 
an  atom  of  sulphur,  or  as  a  compound  of  the  group  CS  with  one  atom  of 
oxygen. 

255.  In  the  combining  power  of  its  atoms,  silicon  resembles  carbon.  It  also 
is  tetratomic,  as  we  can  understand  from  the  composition  of  the  silicon  com- 
pounds which  we  have  studied ;  but  there  is  no  monoxide  corresponding  to 
carbon  monoxide,  and  silicon  does  not  appear  to  be  diatomic  in  any  com- 
pounds. 

0=Si=0  HO-Si-OH  F-Si-F 

11  A 

0  FF 

Silicic  oxide.  Silicic  hydrate.  Silicon  fluoride. 

256.  Cyanogen,  C2N2. — We  put  into  a  test-tube  some  mer- 
curic cyanide,  a  white  and 
very  poisonous  compound  of 
mercury,  carbon,  and  nitrogen ; 
then  we  adapt  to  our  test-tube 
a  cork  in  which  we  have  fitted 
a  bent  tube  bearing  a  little 
bulb  containing  some  small 
pieces  of  the  metal  potassium 
(Fig.  81);  the  outer  end  of 
this  tube  is  drawn  into  a  fine 
jet.  We  now  heat  the  mer- 
curic cyanide,  and  presently  metallic  mercury  begins  to  deposit  in 


FIG.  81. 


CYANOGEN.  165 

the  cooler  part  of  the  tube,  and  a  gas  is  escaping  from  the  jet : 
we  light  it,  and  it  burns  with  a  beautiful  peach-blossom-colored 
flame. 

This  gas  is  cyanogen.  It  is  a  colorless  gas,  having  an  odor 
like  that  of  bitter  almonds,  and  is  quite  poisonous.  Its  density 
compared  to  air  is  1.8064,  or  compared  to  hydrogen,  26;  its 
molecular  weight  is,  then,  52,  and  analysis  has  shown  that  it  con- 
tains carbon  and  nitrogen  in  the  proportions  indicated  for  one 
atom  of  each.  Since  its  molecular  weight  is  52,  a  molecule  of 
cyanogen  gas  must  contain  two  atoms  of  carbon  and  two  of  nitro- 
gen. Cyanogen  is  converted  into  a  liquid  by  pressure  or  by  a 
temperature  of — 20.7°.  It  dissolves  in  about  one-quarter  its 
volume  of  water,  but  the  solution  soon  decomposes,  and  then 
always  contains  ammonia  or  some  ammonium  compound.  The 
combustion  of  cyanogen  produces  nitrogen  and  carbon  dioxide. 

257.  By  the  aid  of  a  spirit-lamp,  we  now  heat  the  bulb  con- 
taining the  potassium.  There  is  a  bright  flash  of  light :  the 
potassium  and  cyanogen  have  combined,  and  formed  potassium 
cyanide.  Cyanogen  is,  then,  capable  of  entering  into  combination. 
When,  however,  we  analyze  the  potassium  cyanide  formed,  we 
find  that  it  contains  potassium,  carbon,  and  nitrogen  in  the  pro- 
portions required  for  one  atom  of  each ;  its  formula  is  KCN. 
The  cyanogen  molecule  C2N2  has  then  separated  into  two  groups 
CN,  each  of  which  has  combined  with  an  atom  of  potassium. 
The  group  CN  is  a  radical,  and  free  cyanogen  resembles  free  chlo- 
rine in  this  respect,  for  the  molecule  of  chlorine  contains  two 
atoms,  while  the  molecule  of  cyanogen  contains  two  groups  or 
radicals. 

Cl-Cl  NC-CN 

The  reaction  between  potassium  and  cyanogen  is,  then,  like  that 
between  potassium  and  chlorine ;  both  are  double  decompositions. 

K-K  +  Cl-Cl  =  KC1    +  KC1 

K-K  +  (CN)-(CN)  =  KCN  +  KCN 

258.  In  free  cyanogen  gas  is  it  the  carbon  atoms  which  are  united  together, 
or  the  nitrogen  atoms  ?  When  cyanogen  or  its  compounds  decompose,  the  ni- 
trogen atoms  always  form  compounds  in  which  they  are  triatomic,  having  the 
combining  power  of  three  atoms  of  hydrogen.  Then  we  must  believe  that  they 


166  LESSONS   IN   CHEMISTRY. 

are  also  triatomic  in  cyanogen,  and  since  the  carbon  atom  is  worth  four  hydro- 
gen atoms  and  the  nitrogen  atom  only  satisfies  three-fourths  of  this  combining 
power,  the  carbon  atoms  must  be  united  together,  and  we  consequently  write 
cyanogen  gas  NEC-CEN  or  (CN)2.  We  see  also  that  the  potassium  atom  in 
potassium  cyanide,  and  the  mercury  atom  in  mercuric  cyanide,  must  be  united 
to  the  carbon  atom  of  cyanogen.  (Compare  $$  262  and  334.) 

K-CEN  NEC-Hg-CEN 

Although  carbon  and  nitrogen  do  not  combine  directly,  potassium  cyanide 
is  formed  when  either  nitrogen  gas  or  ammonia  is  passed  over  a  highly-heated 
mixture  of  charcoal  with  potassium  carbonate  or  potassium  hydroxide.  All 
the  compounds  of  cyanogen  are  prepared  from  potassium  ferrocyanide  ($266). 


LESSON    XXXII. 
HYDROCYANIC  ACID.— CYANIDES. 

259.  Hydrocyanic  Acid,  HCN. — This  dangerous  poison,  com- 
monly called  prussic  acid,  is  formed  when  a  cyanide  is  treated 
.with  a  dilute  acid ;  as  by  the  action  of  hydrochloric  acid  on  mer- 
curic cyanide. 

Hg(CN)2        +        2HC1        =        HgCl2        +        2HCN 
Mercuric  cyanide.  Mercuric  chloride. 

It  is  usually  made  by  distilling  8  parts  of  potassium  ferrocya- 
nide with  a  cooled  mixture  of  9  parts  of  sulphuric  acid  and  14 
parts  of  water.  The  beak  of  the  retort  containing  this  mixture  is 

inclined  upwards,  in  order 
that  the  water  may  condense 
and  run  back  into  the  retort ; 
the  vapor  of  hydrocyanic  acid 
is  dried  by  passing  through  a 
calcium  chloride  tube  placed 

FIG  82  *n  water  heated  to  about  30°, 

and  then  condensed  in  a  flask 
surrounded  by  a  mixture  of  ice  and  salt  (Fig.  82). 

260.  Hydrocyanic  acid  is  a  colorless,  very  volatile  liquid ;  its 
odor  resembles  that  of  bitter  almonds.     Its  density  is  about  0.7  ; 


HYDROCYANIC   ACID.  167 

it  freezes  at  — 15°,  and  boils  at  26.5°.  The  density  of  its  vapor 
compared  to  hydrogen  is  13.5,  corresponding  exactly  with  the 
molecular  weight  implied  by  the  formula  HON.  It  dissolves  in 
all  proportions  of  water,  and  a  two  per  cent,  solution  is  used  in 
medicine.  It  is  combustible,  and  when  ignited  burns  into  water, 
carbon  dioxide,  and  nitrogen.  It  is  exceedingly  poisonous,  and 
the  accidental  inhalation  of  its  vapor  has  in  some  cases  proved 
fatal. 

261.  It  is  often  important  to  be  able  to  recognize  hydrocyanic 
acid ;  and  we  may  do  so  by  the  following  tests.  We  -make  our 
solution  of  hydrocyanic  acid  for  these  tests  by  adding  a  little  dilute 
sulphuric  acid  to  some  solution  of  potassium  cyanide.  The  liquid 
then  contains  hydrocyanic  acid  and  potassium  sulphate. 

Over  the  beaker  glass  in  which  we  have  prepared  this  solution, 
we  invert  a  watch-glass  or  glass  plate  on  which  we 
have  placed  a  drop  of  silver  nitrate  solution  (Fig. 
83) :  this  drop  soon  becomes  clouded  from  the  for- 
mation of  insoluble  silver  cyanide ;  the  white  de- 
posit does  not  darken  quickly  on  exposure  to  light,  and 
leaves  metallic  silver  when  heated ;  these  characters 
distinguish  it  from  silver  chloride,  which  would  be       pIG  §3. 
formed  if  the  liquid  contained  hydrochloric  acid. 

We  now  invert  over  our  beaker  another  watch-glass  containing 
a  drop  of  ammonium  sulphide  which  has  become  yellow  by  expo- 
sure to  light  and  air:  some  ammonia  has  escaped  from  it,  and  it 
contains  an  excess  of  sulphur.  In  a  little  while  this  drop  becomes 
colorless :  a  compound  called  ammonium  sulphocyanate  has  been 
formed  in  it. 

(NH*)*S    -I-    S2     +    2HCN    -     2NH*SCN    +    IPS 
Ammonium  Ammonium 

sulphide.  sulphocyanate. 

If  we  now  carefully  warm  the  spot  until  it  no  longer  has  the  odor 
of  hydrogen  sulphide,  and  then  touch  it  with  a  drop  of  ferric 
chloride  solution,  a  blood-red  color  appears.  This  color  is  due  to 
the  formation  of  ferric  sulphocyanate  (§  277). 

We  mix  in  a  test-tube  a  few  drops  of  our  hydrocyanic  acid 


168  LESSONS   IN   CHEMISTRY. 

solution  with  a  little  ferrous  sulphate  and  ferric  sulphate,  and  add 
a  little  strong  solution  of  sodium  hydroxide :  a  dirty  deposit  forms, 
but  when  we  add  an  excess  of  hydrochloric  acid,  a  part  of  the 
deposit  is  dissolved,  and  a  fine  blue  precipitate,  Prussian  blue 
(§  267),  remains. 

262.  Hydrocyanic  acid  does  not  keep  long,  soon  decomposing,  whether  it  be 
pure  or  in  solution.  It  undergoes  an  interesting  reaction  with  strong  hydro- 
chloric acid,  and  the  reaction  is  more  interesting  because  it  is  characteristic 
of  all  the  cyanides.  When  we  mix  hydrocyanic  acid  with  strong  hydro- 
chloric acid,  the  mixture  becomes  hot,  and  a  mass  of  crystals  of  ammonium 
chloride  separate.  The  most  curious  part  of  this  reaction  is,  that  it  takes 
place  between  the  hydrocyanic  acid  and  the  water  of  the  hydrochloric  acid ; 
the  nitrogen  atom  of  the  former  is  exchanged  for  an  atom  of  oxygen  and  a 
hydroxyl  group. 

HCN     +     2H2Q     =     HCO.OH     +     NH3 

The  ammonia  formed  combines  with  the  hydrochloric  acid.  The  compound 
HCO.OH  is  called  formic  acid.  When  a  solution  of  potassium  cyanide  is 
boiled,  it  is  converted  into  potassium  formate  by  a  similar  reaction. 

KCN         +         2H2Q        «=        HCO.OK         +        NH3 
Potassium  cyanide.  Potassium  formate. 

All  the  acids  of  carbon  which  we  shall  presently  have  occasion  to  study, 
may  be  formed  by  the  replacement  of  the  nitrogen  atoms  of  corresponding 
cyanides  by  an  oxygen  atom  and  a  hydroxyl  group. 

263.  Potassium  Cyanide,  KCN,  is  made  by  heating  dry  po- 
tassium ferrocyanide  red  hot  in  earthen  retorts.     After  the  mass 
cools,  it  is  extracted  with  alcohol,  and  when  the  filtered  liquid  is 
evaporated  it  leaves  a  white  mass  of  potassium  cyanide.     It  is 
very  soluble  in  water,  and  may  be  crystallized  in  cubes.     Upon 
heating  with  sulphur,  it  is  converted  into  potassium  sulpho- 
cyanate,  KS.CN.     Solutions  of  potassium  cyanide  dissolve  the 
cyanides  of  gold,  silver,  zinc,  and  other  metals,  forming  double 
cyanides,  and  some  of  these  also  result  when  the  free  metals, 
in  a  finely  divided  state,  are  treated  with  potassium  cyanide. 
Hence  this  salt  is  extensively  used  in  the  extraction  of  the 
precious  metals  from  their  ores,  in  photography,  and  in  electro- 
plating.    Potassium  cyanide  is  exceedingly  poisonous. 

264.  Silver  Cyanide,  AgCN,  is  formed  as  a  white  precipitate 
when  a  solution  of  silver  nitrate  is  treated  with  the  exact  quan- 
tity of  potassium  cyanide  required  for  one  molecule  of  each. 
When  heated,  it  decomposes  into  silver  and  cyanogen  gas. 


CYANIDES.  169 

•265.  Mercuric  Cyanide,  Hg(CN)2.  —  This  compound  may  be 
made  by  dissolving  mercuric  oxide  in  dilute  hydrocyanic  acid, 
but  it  is  usually  prepared  by  boiling  a  mixture  of  one  part  of 
potassium  ferrocyanide,  two  parts  of  mercuric  sulphate,  and 
eight  parts  of  water.  The  mixture  is  filtered  while  boiling,  and 
mercuric  cyanide  separates  from  the  nitrate  in  colorless,  anhy 
drous,  square  prisms.  It  dissolves  in  eight  times  its  weight  of 
cold  water. 

266.  Potassium  Ferrocyanide,  K4Fe(CN)6.—  Potassium  fer- 
rocyanide is  the  starting-point  for  the  preparation  of  other  com- 
pounds of  cyanogen.  There  are  a  number  of  processes  for  its 
manufacture  :  the  most  common  of  them  consists  in  heating  waste 
animal  matters  containing  nitrogen,  such  as  blood,  horn,  scraps  of 
skin  and  leather,  with  potassium  carbonate  and  scrap  iron.  After 
the  mass  has  cooled,  it  is  exhausted  with  boiling  water,  and  the 
concentrated  solution  deposits  the  ferrocyanide  in  crystals. 

These  crystals  are  yellow,  and  contain  three*  molecules  of  water 
of  crystallization,  which  may  be  driven  out  by  a  temperature  of 
100°  ;  the  anhydrous  salt  then  remains  as  a  white  powder.  Crys- 
talline potassium  ferrocyanide,  which  is  commonly  called  yellow 
prussiate  of  potash,  dissolves  in  four  times  its  weight  of  cold  or 
twice  its  weight  of  boiling  water,  and  is  insoluble  in  alcohol.  It 
is  not  poisonous. 

The  group  of  atoms  Fe(CN)6  which  it  contains  is  a  radical,  and 
takes  part  in  double  decompositions  without  undergoing  change. 
There  is  a  hydroferrocyanic  acid,  H4Fe(CN)6.  We  add  some 
cupric  sulphate  to  solution  of  potassium  ferrocyanide,  and  a  ma- 
hogany-colored precipitate  of  cupric  ferrocyanide  is  formed,  while 
potassium  sulphate  goes  into  solution. 

2CuSO*     +     K*Fe(CN)«    =     2K2SO* 


Solution  of  potassium  ferrocyanide  causes  the  formation  of 
insoluble  ferrocyanides  in  solutions  of  many  metallic  salts,  and 
the  color  of  the  precipitate  is  a  means  frequently  employed  for 
identifying  the  metals.  With  zinc  sulphate,  we  would  have  zinc 
ferrocyanide,  which  is  white,  thrown  down. 


170  LESSONS   IN   CHEMISTRY. 

When  potassium  ferrocyanide  is  heated  to  redness  in  closed  vessels,  it  is 
converted  into  potassium  cyanide,  while  iron  and  carbon  separate  and  nitro- 
gen is  disengaged.  When  it  is  heated  in  the  air  or  with  certain  oxidizing 
agents,  it  yields  potassium  cyanate,  KOCN.  Under  the  same  circumstances 
with  sulphur  it  forms  potassium  sulphocyanate,  KSCN. 

267.  Prussian  Blue,  Ferric  Ferro  cyanide,  (Fe2)2(FeC6N6)3. 
—When  ferrous  sulphate,  FeSO4,  is  added  to  a  solution  of  potas- 
sium ferrocyanide,  the  atom  of  iron  changes  place  with  two  atoms 
of  potassium,  and  a  pale-blue  precipitate  containing  FeK2Fe(CN)6 
is  formed.  When,  however,  potassium  ferrocyanide  is  added  to  a 
ferric  salt,  such  as  ferric  chloride,  FeCP,  a  dark-blue  precipitate 
of  Prussian  blue  is  thrown  down.  As  each  atom  of  iron  in 
ferric  chloride  replaces  three  atoms  of  hydrogen  in  as  many 
molecules  of  hydrochloric  acid,  it  will  also  replace  three  atoms 
of  potassium,  and  we  must  write 


4FeCl3        +        3K*Fe(CN)6  12KC1     + 

Ferric  chloride.        Potassium  ferrocyanide.  Prussian  blue. 

Prussian  blue,  much  used  as  a  pigment,  generally  comes  in 
cubical  masses  having  a  coppery  reflection.  It  is  insoluble  in 
water,  and  in  dilute  acids,  with  the  exception  of  solutions  of  oxalic 
acid.  It  is  dissolved  by  alkaline  hydroxides,  which  destroy  its  color. 

While  we  are  uncertain  of  the  exact  relations  of  the  atoms  in  the  mole- 
cules of  the  ferrocyanides,  yet  we  have  learned  that  they  contain  a  distinct 
radical,  ferrocyanogen,  Fe(CN)6;  and  we  see  that  the  relations  of  the  atom  of 
iron  in  this  radical  are  quite  different  from  those  of  the  four  iron  atoms  in 
Prussian  blue.  The  latter  readily  leave  and  re-enter  the  molecule  by  double 
decomposition,  but  the  iron  atom  in  ferrocyanogen  always  goes  with  the  six 
groups,  CN,  unless  the  molecule  be  decomposed  by  heat  or  energetic  chemical 
agents. 

268.  Potassium  Ferricyanide,  K3Fe(CN)6.—  This  compound 
is  formed  by  passing  chlorine  gas  into  a  solution  of  potassium 
ferrocyanide.  The  chlorine  removes  one  atom  of  potassium 
from  each  molecule  of  the  ferrocyanide,  thereby  converting  the 
iron  into  the  ferric  state. 


2K*FeC6N6         +         Cl2        =         2KC1          + 
Potassium  ferrocyanide.  Potassium  ferricyanide. 


The  salts  are  separated  by  crystallization. 


POTASSIUM   ISOCYANATE.  171 

Potassium  ferricyanide  forms  beautiful,  large,  ruby-red,  anhy- 
drous crystals.  It  dissolves  in  about  four  times  its  weight  of  cold 
water,  and  the  solution  has  a  greenish-brown  color.  It  forms  no 
precipitate  with  ferric  salts,  but  with  ferrous  sulphate  gives  a  dark- 
blue  precipitate  of  ferrous  ferricyanide,  called  Turnbull's  blue. 

2K3FeC6N«  +          SFeSO4          -     3K2SO*     +     Fe3(FeC6N<5)2 

Potassium  ferricyanide.        Ferrous  sulphate.  Turnbull's  blue. 


LESSON    XXXIII. 

CYANATES   AND    UREA. 

269.  Potassium  Cyanate,  KO.CN. — When  an  intimate  mix- 
ture of  perfectly  dry  potassium  ferrocyanide  with  half  its  weight 
of  manganese  dioxide  is  heated  to  dull  redness  with  constant 
stirring,  the  mixture  becomes  black  and  pasty.     The  potassium 
ferrocyanide  has  been  decomposed,  and  potassium  cyanate  ex- 
ists in  the  product.     To  extract  this  substance,  the  black  mass 
is  finely  powdered  and  the  powder  shaken  up  with  boiling  eighty 
per  cent,  alcohol :  the  liquid  is  quickly  decanted  from  the  sedi- 
ment, and  on  cooling  deposits  potassium  cyanate  in  small,  color- 
less, anhydrous   crystals.      It  is  very  soluble  in  water ;  only 
slightly  soluble  in  cold  alcohol.     When  the  aqueous  solution  is 
heated,  the  cyanate  is  decomposed  into  potassium   carbonate, 
carbon  dioxide,  and  ammonia. 

2KO.CN        +        3H20        =        K2C03        +        CO2        +        2NH» 

Potassium  cyanate  is  decomposed  in  the  same  manner  by 
acids  :  hydrochloric  acid  converts  it  into  potassium  chloride  and 
ammonium  chloride,  while  carbon  dioxide  escapes  with  efferves- 
cence. 

KO.CN     +     2HC1     +     H20     =     KC1     +     NH*C1     +     CO2 

270.  The  acid  corresponding  to  potassium  cyanate  is  of  course 
cyanic  acid,  HO.CN,  but  it  cannot  be  made  by  double  decom- 


172  LESSONS    IN    CHEMISTRY. 

position  with  potassium  cyanate.     It  has  been  obtained,  how- 
ever, by  distilling  cyanuric  acid*  N3C303H3. 

N3C3(OH)3        =        3HO.CN 

Cyanic  acid  is  very  unstable  :  at  ordinary  temperatures  it  rapidly 
changes  into  an  amorphous  substance  called  cyamelide. 
The  most  interesting  salt  of  cyanic  acid  is 

271.  Ammonium  Cyanate,  NH4O.CN,  which  is  formed  when 
vapor  of  cyanic  acid  is  mixed  with  ammonia  gas.     It  is  a  white 
solid,  very  soluble  in  water.    When  its  aqueous  solution  is  boiled, 
or  even  left  to  itself  for  a  few  days,  the  ammonium  cyanate  is 
converted  into  another  substance  of  the  same  molecular  compo- 
sition, CON2H4,  called  urea. 

272.  In  order  to  explain  this  fact,  that  two  substances  may 
be  represented  by  the  same  formula  and  yet  have  entirely  dif- 
ferent properties,  we  must  believe  that  the  atoms  are  differ- 
ently arranged  within  their  molecules.     Such  compounds  are 
said  to  be  isomeric,  and  to  possess  different  molecular  structure. 
The    structural    formulae    we    employ   are    deduced   from   the 
modes  of  formation,  and  the  decompositions  of  the  compounds 
they  represent.     Isomeric  bodies  are  very  common  among  the 
carbon  compounds. 

273.  Urea,  CO(NH2)2,  may  be  formed  by  a  reaction  which 
establishes  its  molecular  structure  beyond  doubt.     When  car- 
bonyl  chloride,  COC12,  is  made  to  react  with  ammonia,  urea  and 
hydrochloric  acid  are  formed. 

COCl2        +         2NH3        =        CO(NH2)2        +        2HC1 
Carbonyl  chloride.  Urea. 

Here  two  molecules  of  ammonia  lose  each  one  atom  of  hydro- 
gen, which  combines  with  the  chlorine  of  the  carbonyl  chloride, 


*  Cyanuric  acid  is  a  white  crystalline  body  which  is  formed  by  heating  urea, 
and  by  the  action  of  water  on  the  solid  chloride  of  cynogen,  C3N3C13.  This 
latter  results  from  the  action  of  chlorine  upon  hydrocyanic  acid  in  direct  sun- 
light. 

3HCN         +         3d2        =         C3N3C13         4-         3HC1 


AMMONIUM    CYANATE.  173 

and  the  unsatisfied  groups  CO  and  2NH2  combine,  forming  a 
molecule  of  urea.  The  group  NH2  passes  readily  from  one  mole- 
cule to  another  by  double  decomposition.  It  represents  a  molecule 
of  ammonia  from  which  an  atom  of  hydrogen  has  been  removed : 
it  is  a  monatomic  radical.  We  may  then  consider  that  urea  is 
formed  from  two  molecules  of  ammonia  by  the  replacement  of 
one  atom  of  hydrogen  of  each  by  the  diatomic  radical  carbonyL 
Compounds  formed  by  the  replacement  of  the  hydrogen  atoms  of 
ammonia  by  other  atoms  or  groups  are  called  amines  or  amides : 
when  the  replacement  is  by  the  radicals  of  acids,  the  name  amide 
is  used  to  designate  the  new  compound,  while  amine  is  applied  to 
such  compounds  as  result  from  the  replacement  of  these  hydrogen 
atoms  by  radicals  which  are  also  capable  of  replacing  the  hydrogen 
of  acids.  Since  carbonyl  is  the  radical  of  carbonic  acid,  which 
is  carbonyl  dihydrate,  CO(OH)2,  we  call  urea  carbonyl  amide,  or 
carbamide. 

274.  We  have  already  learned  that  urea  is  formed  by  a  curious 
change  which  takes  place  in  ammonium  cyanate.  Since  we  can 
readily  prepare  potassium  cyanate,  we  have  a  ready  means  of 
obtaining  urea.  For  this  purpose  potassium  cyanate  is  pre- 
pared as  has  already  been  described  (§  269) ;  but,  instead  of 
exhausting  the  mass  with  alcohol,  we  exhaust  it  with  cold  water, 
which  dissolves  out  the  cyanate.  The  solution  is  then  mixed 
with  ammonium  sulphate  in  quantity  equal  to  five-sevenths  of 
the  potassium  ferrocyanide  used,  and  the  whole  is  evaporated  to 
dryness  on  a  water-bath.  The  ammonium  sulphate  reacts  with 
the  potassium  cyanate,  forming  potassium  sulphate  and  ammo- 
nium cyanate,  and  the  latter  becomes  converted  into  the  isomeric 
compound,  urea.  The  mixture  of  the  two  bodies  is  extracted 
with  a  small  quantity  of  boiling  alcohol,  which  does  not  dissolve 
the  potassium  sulphate,  but  dissolves  the  urea,  and  on  cooling 
deposits  it  in  crystals. 

The  formation  of  urea  from  ammonium  cyanate  was  discovered  by  Woehler 
in  1828.  It  was  the  first  instance  of  the  production  of  an  "  organic"  com- 
pound from  a  body  of  mineral  origin  by  chemical  means.  Before  that  time 
it  was  held  that  compounds  found  in  plants  and  animals — organic  compounds 
— could  not  be  formed  except  under  the  influence  of  a  vital  force. 


174  LESSONS   IN    CHEMISTRY. 

2*75.  Urea  is  the  principal  solid  constituent  of  the  urine:  it 
is  in  this  compound  that  the  greater  part  of  the  nitrogen  of 
burned  tissues  is  removed  from  the  body.  It  may  be  extracted 
from  urine  by  evaporating  the  liquid  to  a  thick  syrup,  and  adding 
nitric  acid  when  it  has  cooled.  The  nitric  acid  combines  with 
the  urea,  forming  urea  nitrate,  CO(NH2)2.HN03,  which  separates 
in  a  mass  of  crystals.  These  are  drained,  and  treated  with 
barium  carbonate  as  long  as  there  is  effervescence.  The  mix- 
ture is  then  evaporated  to  dryness,  and  the  urea  is  dissolved 
from  the  barium  nitrate  by  boiling  alcohol. 

276.  Urea  forms  colorless  crystals  having  a  cooling  taste.     It 
dissolves  in  its  own  weight  of  water,  and  in  five  times  its  weight 
of  cold  alcohol ;  it  is  very  soluble  in  boiling  alcohol.    An  aqueous 
solution  of  chlorine  instantly  decomposes  it,  setting  free  nitrogen 
and  carbon  dioxide. 

CO(NH2)2     +     H20     +     3C12    =     CO2     +     N2     +     6HCI 

By  the  action  of  heat,  its  solution  in  water  is  converted  into 
ammonium  carbonate. 

CO(NH2)2     +     2H20    =     (NH*)2C03 

The  same  reaction  takes  place  slowly  in  urine,  and  accounts  for 
the  ammoniacal  odor  of  stale  urine. 

277.  Potassium  Thiocyanate  or  Sulphocyanate,  KS.CN. — 
A  mixture  of  potassium  ferrocyanide  with  half  its  weight  of 
flowers  of  sulphur  is  heated  to  dull  redness  in  a  covered  cruci- 
ble.    After  cooling,  the  mass  is  dissolved  in  water,  the  liquid  is 
filtered,  and  potassium  carbonate  is  added  as  Ions:  as  it  causes 
any  precipitate.     Then  the  liquid  is  again  filtered,  and  the  solu- 
tion evaporated  to  dryness.     The  residue  is  extracted  with  hot 
alcohol,  and  the  alcoholic  solution  allowed  to  evaporate.     Potas- 
sium thiocyanate  then  separates  in  colorless,  deliquescent  crys- 
tals which  are  very  soluble  in  water  and  in  alcohol.     A  solution 
of  potassium  sulphocyanate  produces  a  blood-red  color  (ferric 
sulphocyanate)  with  solutions  containing  ferric  salts. 

Fed3        +        3KS.CN        =        Fe(S.CN)3        +        3KC1 

With  silver  nitrate  it  gives  a  white  curdy  precipitate  which 
is  insoluble  in  nitric  acid. 


METHANE.  175 

Potassium  thiocyanaie  corresponds  to  the  cyanate  in  which 
the  oxygen  atom  is  replaced  by  an  atom  of  sulphur. 

278.  Ammonium  Thiocyanate,  (NH4)S.CN,  is  found  in  small  quantity  in 
the  water  which  has  been  used  to  wash  coal-gas  (§  225).  Representing  am- 
monium cyanate  in  which  the  oxygen  is  replaced  by  sulphur,  it  undergoes  by 
the  action  of  heat  a  similar  curious  change  into  the  isomeric  compound  thio- 
urea,  CS(NH2)2,  whose  molecule  is  exactly  like  that  of  urea,  excepting  that  it 
contains  sulphur  instead  of  oxygen. 


LESSON    XXXIV. 
COMPOUNDS   OF  CARBON  AND  HYDROGEN  (i). 

279.  Methane,  CH4. — In  a  glass  flask  on  a  sand-bath  we  heat 
a  mixture  of  equal  parts  of  dried  sodium  acetate,  sodium  hydroxide, 
and  powdered  lime  (Fig.  84).  The.  lime  does  not  enter  into  the 


FIG.  84. 

reaction  which  takes  place,  but  it  prevents  the  hot  sodium  hydrox- 
ide from  melting  through  the  glass.  Since  gas  will  be  disengage- 1 
we  have  adapted  to  our  flask  a  cork  and  tube,  and  may  collect  this 
gas  over  water,  in  which  it  is  almost  insoluble.  The  gas  is  methane : 
it  is  produced  by  a  reaction  between  the  sodium  acetate  and  sodium 
hydrate,  which  at  the  same  time  yield  sodium  carbonate. 

NaC2H302         +         NaOH         =  Na2C03  +         CH4 

Sodium  acetate.  Sodium  carbonate.  Methane. 


176  LESSONS   IN    CHEMISTRY. 

280.  It  is  a  colorless  gas,  having  no  odor.  Its  density  compared 
to  air  is  0.559,  or  compared  to  hydrogen,  8 :  this  corresponds  to  a 
molecular  weight  of  16,  as  is  indicated  by  the  formula,  CH4.  It 
is  a  combustible  gas,  and  burns  with  a  pale  flame.  It  forms  an 
explosive  mixture  with  air  or  oxygen,  and  this  mixture  is  often 
unfortunately  formed  in  the  galleries  of  coal-mines,  for  methane  is 
the  fire-damp  of  the  miners.  It  exists  under  strong  pressure  in 
the  coal-beds,  and  escapes  when  these  beds  are  cut  into  by  the 
miners. 

We  have  already  learned  that  a  certain  temperature  is  necessary 
for  combustion,  as  indeed  for  all  chemical  action,  and  a  gas  cannot 
continue  burning  when  its  flame  is  cooled  below  the  igniting  point. 
When  a  flame  is  inserted  in  a  tube,  not  too  wide,  it  is  extinguished, 
because  the  walls  of  the  tube  cool  it.  For  this  reason  the  flame 
does  not  run  down  the  tube  of  a  good  Bunsen  burner,  although 
the  combustible  gas  is  mixed  with  air.  A  piece  of  wire  gauze 
may  be  regarded  as  composed  of  a  large  number  of  fine,  short 
tubes,  and  wire  gauze  will  prevent  the  passage  of  flame.  The 
fineness  of  the  gauze  required  will  depend  on  the  igniting  point 
of  the  gas  or  vapor,  and,  as  this  temperature  is  lower,  the  gauze 
must  be  finer.  We  may  depress  a  piece  of  wire  gauze  in  the  flame 
of  a  Bunsen  burner  or  a  lamp,  and  the  flame  is  kept  below  the 
gauze  until  the  latter  is  heated  to  the  temperature  required  for 

the  combustion  of  the  gas. 
Yet  the  combustible  gas 
passes  through,  and  we  may 
light  it  above  the  gauze :  in 
the  same  manner  we  may 
hold  the  gauze  a  short  dis- 
tance above  the  burner  in 
the  escaping  but  unlighted 

FIG.  85.  gas,  and  we  may  ignite  the 

gas  above  the  gauze ;   the 

flame  does  not,  however,  pass  below  until  the  gauze  becomes 
heated  as  before  (Fig.  85).  These  principles  are  applied  in  the 
miners'  safety-lamp,  which  is  practically  a  lamp  so  arranged  that  air 


METHANE. 


177 


can  pass  to  the  flame  and  the  burned  gases  escape  only  through 
the  ineshes  of  fine  wire  gauze  (Fig.  86).  For 
better  illumination,  that  part  of  the  gauze  im- 
mediately around  the  flame  is  usually  replaced 
by  thick  glass.  The  explosive  gases  may  enter 
this  lamp,  and  may  burn  inside,  but  the  flame 
cannot  pass  through  unless  the  gauze  become 
highly  heated.  In  most  countries  it  is  unlaw- 
ful to  continue  working  galleries  containing 
explosive  gases  until  those  gases  are  removed 
by  ventilation.  The  safety-lamp  affords  a 
means  of  detecting  the  presence  of  very  small 
quantities  of  such  gases  without  danger  of  ex- 
ploding them.  We  pass  a  little  illuminating 
gas,  of  which  about  40  per  cent,  is  methane, 
into  an  inverted  jar,  and  mix  it  well  with  the 
air  in  the  jar  by  moving  a  roll  of  paper  around 
in  it.  We  now  push  up  into  the  jar  a  lighted 
wax  taper,  the  end  of  which  projects  just  be- 
yond a  small  glass  tube  slipped  over  it,  so  that 
the  flame  is  quite  small.  We  see  that  this  small 
flame  is  surmounted  by  a  pale  and  tremulous 
bluish  cap  (Fig.  87) :  this  is  owing  to  the 
combustion  of  the  mixture  of  gas  and  air  im- 
mediately around  the  flame,  but  there  is  so 
little  of  the  combustible  gas  present  that  the 
heat  produced  by  its  combustion  immediately  around  the  flame  is 
not  sufficient  to  carry  the  combustion  throughout  the  whole  mix- 
ture ;  otherwise  there  would  be  an  explosion.  By  looking  at  the 
flame  in  his  safety-lamp,  the  miner  can  tell  by  the  presence  or 
absence  of  this  bluish  cap  whether  any  fire-damp  be  present,  and, 
if  so,  whether  there  be  sufficient  to  indicate  danger  of  explosion. 
281.  Methane  is  one  of  the  products  of  the  putrefaction  of 
vegetable  matters  in  presence  of  water.  It  is  formed  by  the  de- 
composition of  such  substances  in  the  muddy  bottoms  of  ponds 
and  rivers,  and  rises  in  bubbles  through  the  water  when  this  mud 

12 


FIG.  86. 


178  LESSONS    IN   CHEMISTRY. 

is  stirred :  it  often  collects  under  the  ice  in  winter,  and  will  escape 
and  burn  with  a  pale  flame  when  the  ice  is  pierced  and  the  gas 
lighted.  Because  of  its  formation  in  these 
localities,  methane  is  often  called  marsh  gas. 

282.  The  composition  of  methane  shows  us  that  the 
carbon  atom  is  tetratomic;  it  has  the  combining  power 
of  four  atoms  of  hydrogen.     We  have  already  learned 
that  chlorine  has  an  energetic  affinity  for  hydrogen, 
and  that  it  will  remove  this  element  from  many  hy- 
drogen   compounds.     When    chlorine    is    mixed   with 
methane,  and  the  mixture   is   exposed  to  light,  the 
chlorine  removes  the  hydrogen  from  the  methane,  and 
hydrochloric  acid  is  formed,  but  an  atom  of  chlorine 
takes  the  place  of  every  atom  of  hydrogen  so  removed. 
We  may  consider  that  there  is  a  double  decomposition 
FlG.  87.         *    between  the  chlorine  molecules  and  the  methane  mole- 
cules, and  this  decomposition  may  continue  until  all 
the  hydrogen  atoms  of  the  methane  are  replaced  by  chlorine. 
CH4     +     Ci2       =     CH3C1      +     HC1 
CH*     +     2C12     -     CHW    +     2HC1 
CH4     +     3C12    =     CHC13     +     3HC1 
CH*     +     4C12     =     CC1*         +     4HC1 

All  these  compounds  of  carbon  with  chlorine  and  hydrogen  may  thus  be  ob- 
tained by  substitution.  Their  compositions  are  a  still  further  evidence  that 
the  carbon  atom  is  tetratomic.  The  hydrogen  atoms  of  methane  may  also  be 
replaced  by  the  monatomic  atoms  of  bromine  and  iodine,  producing  compounds 
precisely  similar  to  those  formed  by  chlorine. 

One  of  the  substances  so  formed  has  the  composition  CH3I;  it  is  called 
methyl  iodide,  and  the  compound  CH3C1  is  called  methyl  chloride.  We  may 
consider  that  the  group  oT  atoms  CH3  acts  like  a  single  atom  as  potassium  in 
potassium  chloride  ;  and  when  we  have  learned  that  it  may  take  part  in  double 
decompositions,  leaving  one  molecule  and  entering  another  without  change, 
we  shall  see  that  it  is  a  radical;  it  is  called  methyl. 

283.  Methyl  iodide,  CH3I,  is  a  colorless  liquid.  When  it  is 
sealed  up  in  strong  glass  tubes  containing  some  zinc,  and  the 
tubes  are  heated  for  a  time  to  about  150°,  the  zinc  takes  away 
the  iodine  from  the  methyl  iodide,  and  zinc  iodide,  Znl2,  is 
formed.  When  the  tubes  are  carefully  opened,  they  are  found  to 
contain  a  gas  to  which  both  analysis  and  density  assign  the  com- 
position C2H6.  How  must  the  atoms  be  related  in  a  molecule  of 
this  gas  ?  Are  the  carbon  atoms  still  tetratomic  ?  How  has  the 


COMPOSITION    OF   HYDROCARBONS.  179 

gas  been  formed  ?  We  must  believe  that  when  two  atoms  of 
iodine  are  removed  from  two  molecules  of  methyl  iodide  the  two 
monatomic  methyl  groups,  CH3,  combine  together ;  that  in  a  mol- 
ecule of  the  gas,  C2H6,  the  two  carbon  atoms,  each  with  its  three 
hydrogen  atoms,  like  three  satellites,  form  a  perfect  system.  We 
can  represent  this  relation  by  our  formulae. 

CH3I          +          Zn        +          ICH3       =      Znl2       +       H3C-CH8 
Methyl  iodide.  Zinc.  Methyl  iodide.      Zinc  iodide.  Ethane. 

Then  in  this  gas,  C2H6,  which  is  called  ethane,  the  affinity  of 
the  carbon  atoms  must  be  satisfied  partly  by  their  combination 
together,  and  partly  by  their  combination  with  hydrogen. 

284.  By  the  action  of  chlorine  on  ethane,  the  hydrogen  of  that 
gas  may  be  replaced  by  chlorine  atoms,  and  compounds  may  also 
be  obtained  in  which  the  replacement  is  by  iodine  atoms.  When 
only  one  of  the  hydrogen  atoms  is  so  replaced,  the  compound 
C2H5I  is  formed.  We  consider  that  this  contains  the  radical 
C2H5,  which  is  called  ethyl,  and  the  molecule  C2H5I  is  called 
ethyl  iodide.  Since  all  the  atoms  of  hydrogen  in  a  molecule  of 
ethane  must  have  the  same  relations  to  the  carbon  atom  around 
which  they  move,  and  also  to  the  other  carbon  atom,  it  is  a  matter 
of  indifference  which  one  we  suppose  to  be  replaced  by  the  iodine 
atom.  When  ethyl  iodide  and  methyl  iodide,  in  the  proportions 
required  for  the  same  number  of  molecules  of  each,  are  heated 
with  zinc  in  sealed  tubes,  a  reaction  takes  place  just  as  in  the  case 
of  zinc  and  methyl  iodide  alone.  That  is,  both  iodine  atoms  are 
removed,  and  we  may  say  either  that  the  iodine  of  ethyl  iodide 
is  replaced  by  the  group  methyl,  CH3,  or  that  the  iodine  of  methyl 
iodide  is  replaced  by  the  radical  ethyl,  C2H5.  A  gas  called  pro- 
pane, C3H8,  is  then  formed. 

C2H5I        +        Zn     +     ICH3        =        ZnP       +     C»HM3H» 
Ethyl  iodide.  Methyl  iodide.        Zinc  iodide.  Propane. 

We  find,  then,  that  the  atoms  of  carbon  are  able  to  combine  to- 
gether; that  they  form  complex  systems  in  which  each  carbon  atom 
is  accompanied  by  atoms  of  hydrogen  or  some  other  element. 
As  we  have  done  before,  we  may  compare  the  carbon  atoms  to 
stars  or  suns  which  revolve  around  each  other ;  each  sun  is  ac- 


180  LESSONS   IN   CHEMISTRY. 

companied  by  its  own  planets,  and  we  shall  presently  see  that 
each  of  the  planets  may  have  its  satellites. 

By  reason  of  the  property  of  combination  between  its  own 
atoms,  a  property  which  is  not  possessed  in  the  same  degree  by 
the  atoms  of  any  other  element,  carbon  forms  an  almost  infinite 
number  of  compounds.  These  compounds  differ  from  those  of 
the  other  elements  in  this  respect : — while  any  other  element  forms 
a  few  compounds  with  nearly  all  other  elements,  carbon  forms  in- 
numerable compounds  containing  very  few  of  the  other  elements. 
The  more  numerous  of  the  carbon  compounds  contain  only  carbon, 
hydrogen,  oxygen,  and  nitrogen,  but  all  of  the  other  elements 
may,  under  proper  conditions,  be  made  to  form  part  of  these  com- 
pounds. The  carbon  compounds  are  generally  called  organic 
compounds. 

285.  The  compounds  containing  carbon  and  hydrogen  only,  are 
called  hydrocarbons ;  we  have  just  studied  three  of  them,  and  in 
the  molecules  of  each  of  these  the  combining  power  of  the  car- 
bon atoms  is  completely  exhausted.  We  may  express  in  detail 
the  atomic  relations  of  the  three. 

H  HH  H  HH 

H-C-H  H-C-C-H  H-C-C-C-H 

H  HH  HHH 

Methane.  Ethane.  Propane. 

The  union  of  the  carbon  atoms  together  does  not  stop  with  propane,  for  in 
turn  one  of  its  hydrogen  atoms  may  be  replaced  by  a  methyl  group,  and  the 
hydrocarbon,  C4H10,  is  the  result.  In  the  same  manner  this  may  be  converted 
into  C5H12,  and  a  whole  series  of  saturated  hydrocarbons  has  been  obtained. 
When  we  examine  the  composition  of  the  members  of  this  series,  we  see  that 
each  contains  two  more  than  twice  as  many  atoms  of  hydrogen  as  it  does  of 
carbon.  We  may  express  the  composition  of  any  member  of  the  series  by  the 
general  formula  OH2n  +  2,  n  representing  the  number  of  carbon  atoms  in  the 
molecule.  The  names  of  these  compounds  end  in  ane,  and  after  the  fourth 
member,  the  prefix  indicates  the  number  of  carbon  atoms  in  a  molecule. 

CH*,     Methane.  WR™,  Pentane. 

C2H«,    Ethane.  C6H14,  Hexane. 

C3H8,    Propane.  Cm™,  Heptane. 

OHW,  Butane.  C8fli8,  Octane. 

The  first  five  are  gases  at  ordinary  temperatures ;  the  others  are  liquids  of 
which  the  boiling  points  are  higher  as  the  number  of  carbon  atoms  in  the 


PETROLEUM.  181 

molecule  increases,  until,  when  this  number  reaches  sixteen,  the  compounds 
are  solid  at  ordinary  temperatures.  Ordinary  paraffin  is  a  mixture  of  the  solid 
members  of  the  series ;  its  name,  meaning  poor  affinity,  indicates  that  it  does 
not  readily  enter  into  chemical  reactions,  and,  since  this  property  is  common 
to  all  of  the  saturated  hydrocarbons,  the  series  OH2n  +  2  is  often  called  the 
pnraffin  series. 

We  see  that  each  member  of  this  series  contains  one  atom  of  carbon  and  two 
atoms  of  hydrogen  more  than  the  preceding.  Compounds  which  thus  differ 
from  each  other  by  CH2,  or  a  multiple  of  that  symbol,  and  which  have  the 
same  general  chemical  properties,  are  said  to  be  homologous,  and  to  form  a 
homologous  series. 


LESSON    XXXV. 
COMPOUNDS  OP   CARBON  AND  HYDROGEN  (2). 

286.  Petroleum. — Petroleum,  or  rock-oil,  as  the  name  signi- 
fies, has  been  known  from  very  early  history,  but  it  has  been 
marvellously  abundant  in  commerce  only  since  1859,  when  it  was 
found  that  the  oil  would  flow  from  wells  bored  into  the  rock  in 
Northwestern  Pennsylvania.  The  oil  usually  occurs  in  a  loose, 
coarse  sandstone  into  which  it  has  drained  from  its  source  in  other 
rocks.  That  source  is  still  a  matter  of  uncertainty,  but  the  oil 
has  doubtless  been  formed  by  the  decomposition  of  vegetable  and 
perhaps  animal  matters,  long  buried  in  the  earth.  The  depth  to 
which  the  wells  must  be  sunk  varies  with  each  locality ;  some- 
times it  is  only  a  few  feet ;  sometimes  it  may  be  two  or  three 
thousand  feet.  Sometimes  the  oil  begins  to  flow  as  soon  as  the 
oil-bearing  rock  is  penetrated,  but  more  usually  the  interior  press- 
ure is  not  strong  enough  to  raise  the  oil,  and  a  pump  must  then  be 
employed.  Petroleum  is  widely  distributed,  being  met  with  in 
nearly  all  parts  of  the  globe.  The  principal  localities  are  in  the 
Eastern  United  States  and  Canada,  Russia,  Austria,  and  Eastern 
Asia. 

Crude  petroleum  varies  in  color  from  pale  yellow  to  almost 
black  ;  it  usually  has  a  greenish  tint.  It  is  sometimes  quite  fluid, 
sometimes  thick  like  molasses.  Its  density  is  comprised  between 
0.75  and  0.92.  It  is  a  mixture  of  a  large  number  of  hydrocarbons, 


182  LESSONS    IN    CHEMISTRY. 

of  which  those  found  in  American  oil  chiefly  belong  to  the  par- 
affins which  we  have  just  studied.  Indeed,  all  the  saturated 
hydrocarbons,  from  CH4  up  to  C16!!34,  have  been  separated  from 
it ;  the  hydrocarbons  of  the  Russian  oil  belong  to  a  different 
series.  Crude  petroleum  is  not  used  for  illuminating  purposes, 
but  is  refined  by  a  process  called  fractional  distillation.  This 
consists  in  slowly  heating  the  oil  and  collecting  separately  the 
portions  that  pass  off  at  different  temperatures.  That  which 
distils  over  below  70°  is  called  naphtha  ;  the  temperature  is  then 
raised  to  about  150°,  and  the  liquid  condensed  up  to  that  point 
is  benzine :  between  150°  and  280°,  kerosene,  or  illuminating  oil, 
distils  over,  and  that  portion  which  passes  between  280°  and  400° 
is  paraffin  oil  or  lubricating  oil.  Much  paraffin  distils  towards 
the  close  of  the  operation,  and  a  residue  of  coke  remains  in  the 
retort. 

Naphtha  has  a  density  of  about  0.65,  and,  when  purified  from 
its  most  volatile  constituents,  forms  gasoline,  used  in  some  gas- 
machines.  Air  is  blown  through  the  gasoline,  and  becomes  charged 
with  sufficient  of  the  vapor  of  the  volatile  hydrocarbons  to  burn 
with  an  illuminating  flame.  Benzine  has  a  density  of  about  0.702, 
and  boils  at  about  148°.  It  is  used  for  dissolving  oils  and  fats,  and 
instead  of  turpentine  for  mixing  with  paints. 

Kerosene  should  contain  no  product  whose  boiling  point  is 
below  150°,  for  the  vapors  of  the  more  volatile  hydrocarbons  form 
dangerously  explosive  mixtures  with  air.  The  fire-test  by  which 
the  safety  of  the  oil  is  determined,  is  made  by  slowly  heating  the 
oil  in  a  little  dish  on  a  water-bath,  carefully  observing  by  means 
of  a  thermometer  the  temperature  at  which  inflammable  vapors 
are  given  off  and  the  temperature  at  which  the  oil  takes  fire. 
A  lighted  match  is  passed  rapidly  over  the  oil,  about  half  a  cen- 
timetre from  its  surface;  when  the  vapor  burns  with  a  little 
flash,  the  thermometer  marks  the  flashing-point.  A  few  degrees 
above  this,  the  oil  itself  takes  fire.  The  flashing-point  should  not 
be  below  60°,  and  the  burning-point  not  below  65°. 

287.  Paraffin. — The  name  paraffin  is  commonly  applied  to 
that  product  of  the  distillation  of  petroleum  which  solidifies  on 
cooling :  it  is  also  a  product  of  the  destructive  distillation  of  peat 


UNSATURATED  HYDROCARBONS.  183 

and  some  kinds  of  coal.  When  the  last  liquid  portions  of  the  dis- 
tillate of  petroleum  are  cooled  by  ice,  a  considerable  quantity  of 
paraffin  separates.  When  purified,  paraffin  is  a  colorless,  trans- 
parent, or  translucent  mass.  It  is  a  mixture  of  several  members 
of  the  series  of  saturated  hydrocarbons.  Accordingly  as  it  has 
been  prepared  and  purified,  its  melting-point  varies  from  45°  to 
65°.  It  makes  excellent  candles, 

288.  We  have  now  learned  something  about  one  class  of  hydrocarbons,  a 
class  in  which  the  carbon  atoms  cannot  combine  with  any  other  atoms  unless 
they  separate  from  each  other.  It  is  worthy  of  notice  that  they  do  not  sepa- 
rate from  each  other  except  by  the  action  of  the  most  energetic  agents  :  on  the 
contrary,  these  carbon  atoms  remain  combined,  and,  with  as  many  of  their 
accompanying  hydrogen  atoms  as  we  permit  to  remain  with  them,  constitute 
fixed  and  definite  radicals,  which  act  exactly  like  the  atoms  of  elements  having 
the  same  combining  powers.  We  have  noticed  two  of  thes'e  radicals,  methyl 
and  ethyl.  In  order  that  there  may  be  a  uniformity  of  names  for  these  com- 
plex groups,  chemists  have  agreed  to  retain  the  first  syllable  of  the  name  of 
the  saturated  hydrocarbon,  in  the  names  of  all  compounds  derived  from  that 
hydrocarbon.  The  termination  in  yl  has  been  selected  for  the  radicals  which 
we  consider  are  formed  by  the  removal  of  one  atom  of  hydrogen  from  a  satu- 
rated hydrocarbon,  and  then  the  first  word  of  the  name  of  a  compound  will 
show  us  the  hydrocarbon  radical  in  the  molecule,  and  the  last  word  must  indi- 
cate the  atom  or  group  of  atoms  combined  with  that  radical.  We  may  then 
understand  the  composition  of  the  following  bodies  : 

CH*,    Methane.     CH3Br,       Methyl  bromide.       CH3.OH,   Methyl  hydroxide. 
C2H6,  Ethane.       C2H5C1,       Ethyl  chloride.          C2H5.0H,  Ethyl  hydroxide. 
C3H8,  Propane.      C3H'  NH2,  Propyl  amine.  (C3IF)20,  Propyl  oxide. 

When  we  have  once  acquired  definite  ideas  of  what  is  meant  by  a  radical, 
that  it  is  a  group  which  acts  precisely  as  an  atom,  having  continually  the  same 
combining  power  or  atomicity,  leaving  one  molecule  and  entering  another  as  a 
distinct  existence;  then  the  structure  of  these  complex  molecules  becomes  per 
fectly  intelligible,  and  we  need  only  be  acquainted  with  the  radicals  concerned 
in  order  to  be  able  at  once  to  interpret,  by  our  system  of  atomic  groupings,  the 
relations  of  the  atoms  in  the  molecule  of  any  compound. 

289.  TJnsaturated  Hydrocarbons. — We  have  mixed  in  a  glass 
flask  some  alcohol  with  four  times  its  weight  of  strong  sulphuric 
acid,  and,  as  this  mixture  sometimes  froths  very  much  when  we 
heat  it,  we  have  put  in  enough  sand  to  absorb  the  liquid  almost 
entirely.  After  fitting  to  our  flask  a  cork  through  which  pass  a 
delivery-tube,  and  a  safety-tube  in  which  we  put  a  little  mercury 


184  LESSONS    IN   CHEMISTRY. 

or  some  sulphuric  acid,  we  heat  it  on  a  sand-bath.  A  gas  is  dis- 
engaged, and  we  may  collect  it  in  jars  over  the  pneumatic  trough. 

290.  ETHYLENE,  C2H4. — The  gas  which  we  have  prepared  is  a 
hydrocarbon.  It  is  colorless  and  almost  odorless  :  its  density  com- 
pared to  air  is  0.9784,  or  compared  to  hydrogen,  14.  Analysis 
shows  that  it  contains  carbon  and  hydrogen  in  the  proportion  of 
one  atom  of  the  first  to  two  atoms  of  the  second,  and  its  density 
shows  that  its  molecule  must  contain  two  atoms  of  carbon  and  four 
of  hydrogen.  Its  composition  is,  then,  C2H4 :  it  is  called  ethylene., 
It  burns  with  a  brilliant  flame. 

Into  a  jar  of  this  gas  we  pour  a  little  bromine,  and  cause  it  to 
flow  over  the  sides  of  the  jar  :  the  color  of  the  bromine  disappears, 
and  drops  of  an  oily  liquid  are  formed.  This  liquid  has  a  pleasant 
odor,  very  different  from  the  suffocating  vapor  of  the  bromine. 
The  ethylene  has  combined  with  the  bromine  and  formed  this 
liquid,  which  is  called  ethylene  bromide.  The  vapor-density  and 
analysis  of  the  compound  assign  to  its  molecule  the  composition 
C2H4Br2.  Evidently  if  the  molecule  C2H4  can  combine  directly 
with  two  atoms  of  bromine,  it  must  be  a  diatomic  molecule,  capable 
of  manifesting  the  combining  power  of  two  atoms  of  hydrogen. 
Let  us  study  the  reaction  by  which  ethylene  is  formed :  alcohol  is 
ethyl  hydrate,  C2H5.OH  :  sulphuric  acid,  by  its  strong  affinity  for 
water,  converts  it  into  H20  -f-  C2H4.  Then,  in  losing  the  mon- 
atomic  hydroxyl  group  and  an  atom  of  hydrogen,  the  carbon  atoms 
of  alcohol  must  recover  the  combining  powers  of  two  atoms  of 
hydrogen :  this  combining  power  is  manifested  in  the  combination 
of  ethylene  with  bromine,  chlorine,  etc.  If  two  atoms  of  hydrogen 
were  removed  from  a  molecule  of  methane,  CH4,  the  remaining 
group,  CH2,  would  be  diatomic,  and  we  believe  that  a  molecule  of 
ethylene  gas  is  formed  by  the  union  of  two  such  diatomic  groups, 
and  is  expressed  by  the  formula  CH2~CH2;  but  these  atoms 
then  possess  more  energy  than  when  combined  in  the  gas  ethane. 
CH3-CH3,  and  may  develop  that  energy  and  enter  into  direct  com- 
bination with  bromine,  forming  ethylene  bromide,  CH2Br-CH2Br. 

ETHYLENE  CHLORIDE,  CH2C1-CH2C1,  is  formed  when  equal 
volumes  of  chlorine  and  ethylene  are  mixed  in  diffuse  daylight. 


DIATOMIC    HYDROCARBONS.  185 

It  is  a  somewhat  oily  liquid,  and  from  this  character  ethylene  was 
first  called  olefiant  (oil-forming)  gas.     The  chloride  boils  at  82°. 
ETHLYENE  BROMIDE,  CH2Br-CH2Br,  is  made  by  passing  ethy- 
lene gas  into  cooled  bromine.     It  boils  at  131°. 

291.  We  have  seen  that  chlorine  is  capable  of  replacing  the 
hydrogen  of  ethane,  C2H6,  atom  for  atom.     From  the  products  of 
this  reaction  we  can  by  careful   operations  separate  two  liquids 
having  the  composition   C2H4C12,   but   having  entirely  different 
properties.    These  compounds  are  isomeric,  and  we  may  understand 
their  isomerism  when  we  see  that  both  atoms  of  chlorine  may 
replace  hydrogen  atoms  which  are  in  relation  to  the  same  atom 
of  carbon,  forming  the  molecule  CH3-CHC12 ;  or  each  may  replace 
an  atom  of  hydrogen  from  a  group  CH3 ;  the  compound  formed 
in  the  latter  case  would  of  course  be  ethylene  chloride. 

292.  Ethylene  is  only  the  first  member  of  a  long  series  of  hydrocarbons 
which  we  may  consider  are  derived  from  it  by  the  replacement  of  one  or  more 
of  its  hydrogen  atoms  by  the  monatomic  hydrocarbon  radicals  which  we  have 
already  studied.     Each  of  the  compounds  so  formed  is  diatomic :  it  will  com- 
bine directly  with  two  atoms   of  chlorine  or  bromine,  and  may  be  made  to 
combine  with  two  monatomic  radicals  or  with  one  diatomic  radical.   The  names 
of  these  diatomic  hydrocarbons  are  made  to  correspond  with  the  saturated 
hydrocarbons,  from  which  we  may  consider  they  are  derived  by  the  removal 
of  two  atoms  of  hydrogen,  but  the  ane  of  the  name  is  changed  to  ylene.   Ethy- 
lene corresponds  to  ethane,  butylene  corresponds  to  butane.     We  have  here 
our  second  series  of  homologous  compounds,  each  differing  from  the  next  by 
CH2. 

CPU4,  Ethylene.  C5H10,  Amylene  or  pentylene. 

C3H6,  Propylene.  C6H12,  Hexylene. 

C4H8,  Butylene.  C7H14,  Heptylene,  etc. 

On  examination,  we  notice  that  each  molecule  contains  twice  as  many 
atoms  of  hydrogen  as  of  carbon  ;  the  general  formula  for  the  series  is  OH2n. 
The  proportion  of  hydrogen  and  carbon  is  the  same  in  each  member  of  the 
series,  but  the  molecular  weights,  nnd  consequently  the  number  of  atoms  in 
the  molecules,  are  not  the  same.  Bodies  of  which  the  molecules  contain  the 
same  atoms  in  the  same  proportion  but  in  different  numbers  are  said  to  be 
polymeric.  All  of  these  diatomic  hydrocarbons  are  polymeric  ;  the  number 
of  carbon  atoms  and  hydrogen  atoms  in  each  is  an  exact  multiple  of  CH2. 
Because  these  hydrocarbons  combine  directly  with  chlorine  and  bromine, 
forming  oily  liquids,  the  series  is  often  called  the  olefine  series. 

293.  It  has  been  said  that  we  may  consider  these  bodies  as  formed  from 
ethylene  by  the  replacement  of  hydrogen  atoms  by  the  monatomic  radicals, 


186  LESSONS    IN    CHEMISTRY. 

methyl,  ethyl,  etc.  We  must  see  that  this  replacement  may  yield  many  in- 
stances of  isomerism.  If  one  of  the  hydrogen  atoms  of  ethylene  be  replaced 
by  methyl,  we  obtain  propylene. 

CH2=CH2  CH2--CH-CH3 

Ethylene.  Propylene. 

By  the  replacement  of  two  of  the  hydrogen  atoms  by  methyl,  we  may 
obtain  two  different  butylenes,  according  to  the  positions  of  the  replaced  hydro- 
gen atoms,  and  there  is  still  a  third  butylene,  formed  by  the  replacement  of 
one  hydrogen  atom  by  an  ethyl  group. 

CEP  CH.CH3  C(CH3)2  CH(C2H5) 

CH2  CH.CH3  CH2  CH2 

Ethylene.    (a)  Dimethylethylene.  (|3)  Dimethylethylene.       Ethylethylene. 
All  these  hydrocarbons  have  been  obtained  and  studied,  and  their  names 
indicate  the  molecules  from  which  they  are  derived  and  the  radicals  which 
are  substituted  for  the  hydrogen  atoms  in  those  molecules. 

ACETYLENE,  C2H2,  is  the  first  member  of  another  series  of 
unsaturated  hydrocarbons.  We  may  prepare  it  by  pouring 
water  over  calcium  carbide,  a  crystalline  body  which  is  made 
from  lime  and  coke  in  the  electrical  furnace. 

CaC2          +          2H'0  C2H2          +          Ca(OH)2 

Acetylene  is  a  colorless  gas  having  a  characteristic  odor.  It 
is  slightly  soluble  in  water,  and  liquefies  under  great  pressure. 
It  burns  with  a  very  smoky,  luminous  flame.  With  air  or  oxy- 
gen it  forms  a  highly  explosive  mixture.  Acetylene  has  lately 
been  introduced  as  an  illuminant :  it  can  be  made  to  yield  a 
light  of  dazzling  brilliancy. 


LESSON    XXXVI. 

COMPOUNDS  OF  CARBON  AND  HYDROGEN  (3).— 
ANALYSIS  OF  CARBON  COMPOUNDS. 

294.  The  tar  which  condenses  during  the  distillation  of  bitu- 
minous coal  for  the  manufacture  of  gas,  is  an  exceedingly  com- 
plex liquid,  consisting  principally  of  compounds  of  carbon  and 
hydrogen.  Some  of  these  compounds  are  solid,  some  of  them  are 
volatile  liquids.  Since  they  boil  at  different  temperatures,  they 


BENZENE. 


187 


can  be  separated  from  each  other  by  fractional  distillation.  The 
vapors  of  the  substances  are  passed  through  a  tube  which  is 
maintained  at  the  boiling  point  of  the  most  volatile  constituent 
of  the  mixture :  in  this  tube  the  liquids  having  higher  boiling 
points  are  condensed,  and  flow  back  into  the  still,  while  the 
vapor  of  the  more  volatile  liquid  passes  on  and  is  condensed 
separately.  A  simple  laboratory  contrivance 
is  a  rather  wide  tube  on  which  a  couple  of 
bulbs  are  blown ;  this  is  placed  vertically 
in  the  flask  in  which  we  boil  the  mixed 
liquid  (Fig.  88).  The  lower  part  of  the 
tube  becomes  heated  to  the  temperature  of 
the  mixed  vapor,  which  is  between  the  boil- 
ing points  of  the  liquids :  as  some  of  the 
most  easily  condensed  vapor  is  cooled  and 
converted  into  a  liquid,  the  temperature  of 
the  tube  gradually  falls  towards  the  upper 
portion,  and  by  carefully  regulating  the  boil- 
ing, only  the  most  volatile  liquid  passes  from 
the  apparatus.  This  is  indicated  by  a  ther- 
mometer of  which  the  bulb  is  opposite  the 
side-tube. 

295.  Benzene,  C6H6.— The  most  volatile 
constituent  of  coal-tar  is  a  liquid  called  ben- 
zene. It  freezes  at  5.5°,  and  boils  at  80.5°. 
It  does  not  dissolve  in  water,  but  is  soluble 
in  alcohol  and  ether.  It  is  very  inflammable,  and  burns  with 
a  bright  but  smoky  flame.  The  composition  of  its  molecule 
is  C6H6,  and  yet  in  most  of  its  reactions  it  acts  like  a  satu- 
rated hydrocarbon.  We  put  a  few  crystals  of  iodine  into  some 
benzene  in  a  glass  flask,  and  pass  chlorine  through  the  liquid ; 
hydrochloric  acid  gas  is  given  off,  and  the  hydrogen  atoms  of 
the  benzene  are  replaced  by  chlorine. 

C6H6      +      Cl2      =      C6H5C1      +      HCl 

The  iodine  only  helps  to  break  up  the  molecules  of  chlorine. 


FIG.  88. 


188  LESSONS    IN    CHEMISTRY. 

Evidently  the  molecular  structure  of  benzene  must  be  different  from  that  of 
the  other  hydrocarbons  which  we  have  studied,  and  we  can  only  account  for  its 
resemblance  to  the  saturated  hydrocarbons  by  supposing  that  its  carbon  atoms 
are  differently  related.     Of  several  theories  which  have  been  proposed  in  order 
to  explain  the  chemical  behavior  of  benzene,  we  need  only  con- 
HC  sider  one,  which  supposes  that  the  atoms  form  a  complex  sys- 

T     tern,  in  which  each  carbon  atom  is  combined  with  two  other 
carbon  atoms,  and  with  an  atom  of  hydrogen.     The  six  car- 


HC''  CH      ">on  atoms  ^us  f°rm  a  cl°se(l  chain,  and  we  may  represent  this 

\<^  by  a  hexagon,  a  carbon  atom  being  placed  at  each  angle.    The 

CH  fourth  atomicity  of  each  carbon  atom  may  be  supposed  to  form 

a  double  bond  with  one  of  the  adjacent  carbon  atoms. 

296.  All  the  hydrogen  atoms  of  benzene  may  be  replaced  by 
other  atoms  or  radicals,  and,  when  more  than  one  is  so  replaced, 
we  have  interesting  isomeric  compounds,  the  isomerism  depending 
on  the  relations  of  the  carbon  atoms  whose  hydrogen  atoms  are 
affected.     Let  us  suppose,  for  example,  that  two  hydrogen  atoms 
are  replaced  by  two  chlorine  atoms :  experiment  has  shown  that 
three  compounds  may  then  be  formed,  having  precisely  the  same 
composition,  but  different  properties. 

We  can  interpret  this  by  our  theory  and  our  representation  of  the  molecule, 
by  considering  that  while  one  atom  of  chlorine  always  occupies  the  same  place, 
the  position  of  the  other  varies. 

CC1  CC1  CC1 

/\CH 

HCl        JCH  HC,        ,CC1  HC 

CH  CH 

These  formulae  represent  the  three  cases  in  which  two  atoms  of  hydrogen  in 
benzene  are  substituted  by  two  atoms  of  chlorine.  Theory  does  not  indicate 
the  existence  of  other  isomers.  By  different  methods  chemists  have  always 
succeeded  in  producing  three  isomeric  compounds  in  which  two  atoms  of  hy- 
drogen of  benzene  are  replaced  by  other  atoms  or  radicals,  but  they  have 
never  been  able  to  obtain  more  than  three  such  compounds. 

297.  There  are  many  hydrocarbons  which  we  believe  to  be 
derived  from  benzene  by  the  replacement  of  its  hydrogen  atoms 
by  radicals,  such  as  methyl,  ethyl,  etc.    Some  of  these  have  been 
obtained  by  methods  which  allow  no  doubt  as  to  their  constitu- 
tion ;  others  have  not  yet  been  so  formed,  but  certain  of  their 
chemical  reactions  seem  to  show  that  they  also  are  derived  from 
benzene.     These  hydrocarbons  and  many  of  the  bodies  derived 


HC/      \CC1  HC 


TURPENTINE. — NAPHTHALENE.  189 

from  them  have  peculiar  aromatic  odors,  and  for  this  reason  the 
whole  series  of  compounds  which  are  considered  as  benzene  de- 
rivatives is  commonly  called  the  aromatic  series.  Of  these  com- 
pounds we  can  consider  only  a  few. 

298.  Methyl-benzene,  or  Toluene,  C6H5.CH3,  was  first  derived 
from  tolu  balsam.     It  is  now  obtained  from  coal-tar,  and  consti- 
tutes a  considerable  proportion  of  the  benzene  of  commerce.     It 
resembles  benzene,  but  boils  at  110°,  and  does  not  solidify  even 
at  —30°. 

We  can  understand  that  there  may  be  four  isoineric  compounds  formed  by 
the  replacement  of  a  single  hydrogen  atom  of  methyl-benzene,  for  that  replace- 
ment may  affect  either  a  hydrogen  atom  in  one  of  three  places  in  the  phenyl 
group,  C6H5,  or  a  hydrogen  atom  of  the  radical  methyl,  CH3.  ^ 

The  three  isomeric  dimethyl  benzenes,  C6H4!  CH3)2,  are  called  xylenes  :  two  are 
liquids,  and  one  is  a  solid.  Isomeric  with  them  is  also  ethyl-benzene,  C6H5.C2H5. 

299.  Oil  of  Turpentine,  C10H16,  is  a  derivative  of  benzene,  and 
it  is  isomeric  with  a  large  number  of  essential  oils.     The  oils  of 
lemon,  orange,  bergamot,  juniper,  lavender,  and  many  others,  all 
appear  to  have  the  same  molecular  composition,  and  we  must 
believe  that  their  differences  are  due  to  a  different  arrangement 
of  the  atoms  constituting  their  molecules.     These  oils  are  obtained 
by  distilling  with  water  the  leaves  or  other  parts  of  the  plant  con- 
taining them.  It  is  true  that  the  boiling  point  of  each  of  these  oils 
is  much  higher  than  that  of  water,  but  the  steam  of  the  water 
readily  carries  over  the  oil.      The  condensed  liquid  then  sepa- 
rates into  two  layers,  the  lower  being  water,  and  the  upper  and 
lighter  being  the  essential  oil.     Oil  of  turpentine  is  so  made  by 
distilling  with  water  the  crude  turpentine  which  flows  from  in- 
cisions made  in  certain  species  of  pine-trees.     There  are  several 
varieties  of  this  oil,  which  differ  according  to  the  species  of  pine 
tree  which  furnishes  them.     The  density  is  about  0.87,  and  they 
boil  at  about  156°.     Oil  of  turpentine  and  most  of  the  essential 
oils  slowly  absorb  oxygen  from  the  air,  and  are  converted  into 
various  resins. 

300.  Naphthalene,  C10H8,  is  a  solid  hydrocarbon  derived  from 
coal-tar.     It  usually  occurs  as  pearly  scales,  melting  at  79°,  and 
boiling  at  218°.     It  does  not  dissolve  in  water,  and  but  slightly 
in  cold  alcohol.     It  is  soluble  in  boiling  alcohol,  and  crystallizes 


190  LESSONS   IN    CHEMISTRY. 

when  the  solution  cools.  It  is  employed  for  the  manufacture  of 
numerous  beautiful  dye-stuffs,  analogous  to  the  aniline  dyes,  which 
we  will  presently  study. 

301.  Anthracene,  C14H10,  is  one  of  the  least  volatile  hydro- 
carbons obtained  from  coal-tar.  When  pure,  it  forms  beautiful 
transparent  prisms,  which  melt  at  213° ;  its  boiling  point  is  360°. 
It  is  employed  for  the  manufacture  of  alizarin,  a  red  coloring 
matter  which  was  until  within  a  few  years  obtained  only  from 
madder.  The  ability  to  produce  this  dye-stuff  by  purely  chemical 
processes  has  permitted  large  areas  of  land  which  were  formerly 
devoted  to  the  cultivation  of  the  madder-plant  to  be  used  for 
raising  grain.  Besides  this,  chemists  have  been  able  to  prepare 
from  this  same  alizarin  valuable  dye-stuffs  of  other  colors,  and 
there  is  now  a  whole  series  of  anthracene  coloring  matters. 

ANALYSIS  OF  CAKBON  COMPOUNDS. 

302.  The  proportions  in  which  the  elements  exist  in  any  carbon  compound 
are  determined  by  elementary  analysis.  If  the  compound  contains  other  ele- 
ments than  carbon,  hydrogen,  and  oxygen,  its  analysis  requires  several  opera- 
tions :  if  only  these  three  elements  be  present,  the  carbon  and  hydrogen  are 
determined  by  one  operation,  and  the  quantity  of  oxygen  is  the  difference  be- 
tween the  sum  of  the  carbon  and  hydrogen  and  the  total  weight  of  the  substance 
analyzed.  The  analysis  is  conducted  by  mixing  a  weighed  quantity  of  the 
substance  with  pure  and  dry  cupric  oxide  in  a  long  glass  tube,  one  end  of 
which  is  drawn  out  to  a  fine  point  and  sealed.  The  other  end  is  connected 
with  a  small  U-tube  containing  pumice-stone  wet  with  sulphuric  acid,  and  the 
U-tube  is  connected  with  a  bulbed  tube  containing  a  solution  of  potassium 
hydroxide  (Fig.  89).  The  tube  is  heated  to  redness  in  a  long  tube-furnace,  and 
the  oxygen  of  the  cupric  oxide  converts  the  hydrogen  of  the  carbon  com- 
pound into  water,  while  the  carbon  is  burned  into  carbon  dioxide.  The  water 
is  absorbed  in  the  tube  containing  the  pumice  and  sulphuric  acid,  while  tin- 
carbon  dioxide  is  absorbed  by  the  potassium  hydroxide.  Towards  the  close  of 
the  operation,  a  caoutchouc  tube  connected  with  an  oxygen  gas-holder  is 
slipped  over  the  drawn-out  point  of  the  combustion-tube ;  the  oxygen  is  turned 
on,  and  the  point  is  broken  otf  by  pinching  the  end  of  the  tube.  A  current  of 
pure  dry  oxygen  is  then  passed  through  the  red-hot  tube,  and  all  traces  of 
carbon  dioxide  and  watery  vapor  are  forced  through  the  absorption-tubes ;  at 
the  same  time  any  unburned  carbon  is  completely  consumed,  and  the  copper 
from  which  oxygen  has  been  removed  is  again  converted  into  cupric  oxide 
for  another  operation.  The  increased  weight  of  the  U-tube  (j  and  g),  in  which 
water  has  been  absorbed,  is  due  to  the  water,  and  one-ninth  of  the  increase 
will  represent  the  quantity  of  hydrogen  in  the  amount  of  substance  analyzed. 


ANALYSIS    OF   CARBON    COMPOUNDS. 


191 


192  LESSONS    IN    CHEMISTRY. 

The  increased  weight  of  the  bulbed  tube  (h)  is  due  to  carbon  dioxide,  and 
j£;  or  -j^j,  of  this  increase  will  give  us  the  quantity  of  carbon  which  we  wish  to 
determine.  Since  the  current  of  oxygen  would  carry  a  little  vapor  of  water 
out  of  the  bulbed  tube,  and  so  diminish  its  weight,  a  small  tube  (i)  containing 
pumice  and  sulphuric  acid  is  attached,  and  in  this  the  vapor  is  retained;  this 
tube  is  always  weighed  with  the  potash  bulbs. 

Having  determined  the  proportions  of  all  the  elements  in  a  compound,  its 
moiecular  weight  is  calculated  from  its  vapor-density,  or,  if  this  be  not  pos- 
sible, by  other  methods.  Knowing  the  molecular  weight  and  the  propor- 
tion of  each  element  present,  it  is  very  easy  to  fix  the  chemical  formula 
expressing  the  composition  of  the  molecule. 


LESSON    XXXVII. 
ALCOHOLS  (i). 

303.  When   the  iodide  of  a  radical  like   methyl  or  ethyl  is 
heated  with  silver  oxide  and  water,  silver  iodide  is  formed,  and 
the  iodine  of  the  carbon  compound  is  replaced  by  a  hydroxyl 
group. 

2CH3I         +         Ag2Q        +       H2Q      =      2AgI         +         2CH3.OH 
Methyl  iodide.          Silver  oxide.  Silver  iodide.  Methyl  hydroxide. 

A  hydroxide  of  the  hydrocarbon  radical  is  so  formed,  and  these 
hydroxides  constitute  what  are  called  the  alcohols.  We  must  study 
some  of  the  more  important  of  these  compounds. 

304.  Methyl  Alcohol,  CH3.OH.— The  liquid  which  condenses 
during  the  manufacture  of  charcoal  (§  226)  contains  small  quan- 
tities of  a  volatile  liquid  which  can  be  separated  by  careful  frac- 
tional distillation.     This  liquid  is  usually  sold  under  the  name 
methylene  or  wood-spirit.     It  is  impure  methyl  alcohol,  and  is 
used  for  the  manufacture  of  varnishes,  and  for  dissolving  fats  and 
oils.     Methyl  alcohol  has  the  property  of  forming  with  calcium 
chloride  a  crystalline  compound,  and  is  usually  purified  by  satu- 
rating the  wood-spirit  with  calcium  chloride,  and  evaporating  the 


ALCOHOLS.  193 

solution  by  a  gentle  heat  until  it  crystallizes.  The  crystals  are 
dissolved  in  water ;  when  their  solution  is  boiled,  the  compound 
of  methyl  hydrate  and  calcium  chloride  is  decomposed,  and  the 
methyl  alcohol  can  be  separated  by  fractional  distillation. 

Pure  methyl  alcohol  is  a  colorless  liquid,  of  an  odor  resembling 
that  of  common  alcohol.  Its  density  at  0°  is  0.814,  and  it  boils 
at  66.5°.  It  mixes  in  all  proportions  with  water  and  with  ordinary 
alcohol.  It  is  inflammable,  and  burns  with  an  almost  colorless 
flame.  We  throw  a  piece  of  sodium  into  methyl  alcohol :  hydrogen 
is  given  off,  and  the  metal  dissolves :  an  atom  of  sodium  has  re- 
placed the  hydrogen  atom  of  the  group  hydroxyl,  and  sodium 
methylate  is  formed.  The  reaction  is  precisely  like  that  which 
yields  sodium  hydroxide  in  the  reaction  of  sodium  with  water. 
2H-0-H  +  2Na  =  2NaOH  +  H2 

2CH3-0-H        +        2Na         =         2CH3-ONa         +         H2 
Methyl  alcohol.  Sodium  methylate. 

When  methyl  alcohol  is  oxidized  slowly,  an  atom  of  oxygen 
replaces  two  hydrogen  atoms  of  the  methyl  group,  CH3,  and  formic 
acid  results. 

CH3.OH        +        O2        =        H20        +        CHO.OH 
Methyl  hydroxide.  Formic  acid. 

305.  Ethyl  Alcohol,  C2H5.OH.— When  ethylene  gas  is  passed 
into  strong  hydriodic  acid,  direct  combination  takes  place,  and 
ethyl  iodide  is  formed. 

C2H*    +    HI    =    C2H5I 

When  this  ethyl  iodide  is  heated  with  potassium  hydroxide  solu- 
tion, a  double  decomposition  takes  place,  yielding  potassium  iodide 
and  ethyl  alcohol. 

C»H5I    +     KOH    =     KI    +     C2H5.0H 

However,  ethyl  hydroxide,  which  is  ordinary  alcohol,  is  manufactured 
by  a  peculiar  decomposition  of  glucose,  or  some  substance  having 
the  same  composition  as  glucose.  This  decomposition  is  brought 
about  by  a  minute  organism  which  lives  and  multiplies  by  con- 
verting the  glucose  into  carbon  dioxide  and  alcohol.  A  decompo- 
sition due  to  such  an  organized  being  is  called  a  fermentation,  and 
the  organism  is  called  a  ferment.  The  molecule  of  glucose  is 

13 


194  LESSONS    IN    CHEMISTRY. 

expressed  by  the  formula  C6H1206,  and,  although  small  quantities 
of  other  substances  are  produced  during  the  fermentation,  which 
is  caused  by  the  yeast-plant  and  is  called  the  alcoholic  fermenta- 
tion, the  general  change  may  be  represented  by  the  equation 
C6H12Q6    =.     2C2H5.0H     +     2C02 

For  the  manufacture  of  alcohol,  the  product  of  the  fermentation 
is  distilled,  and  the  alcohol  so  separated  from  the  water.  However, 
the  best  apparatus  does  not  give  alcohol  stronger  than  about  ninety- 
five  per  cent.  Pure  or,  as  it  is  commonly  called,  absolute  alcohol 
is  made  by  putting  quick-lime  into  the  strongest  alcohol  of  com- 
merce, and  distilling  the  mixture  after  it  has  stood  several  days. 
By  reason  of  its  strong  affinity  for  water,  the  lime  then  retains  all 
of  that  liquid. 

Pure  alcohol  is  a  colorless  liquid,  having  a  faint  but  pleasant 
odor.  Its  density  at  0°  is  0.8095,  and  it  boils  at  78.4°.  It  mixes 
with  water  in  all  proportions,  and  the  mixture  becomes  slightly 
warm  and  contracts  in  volume.  Alcohol  dissolves  many  substances 
which  are  insoluble  in  water ;  among  these  are  iodine,  the  essential 
oils,  fats,  and  resins.  The  spirits  of  the  pharmacies,  such  as  spirits 
of  ammonia,  are  solutions  of  volatile  substances  in  alcohol ;  tinc- 
tures are  similar  solutions  of  non- volatile  substances. 

Alcohol  is  combustible,  and  burns  with  a  pale  flame,  the  prod- 
ucts of  the  combustion  being  carbon  dioxide  and  water. 

By  the  slow  oxidation  of  alcohol,  acetic  acid  and  a  volatile 
liquid  called  aldehyde  are  formed ;  acetic  acid  by  the  replacement 
of  two  atoms  of  hydrogen  of  the  ethyl  group  by  an  atom  of  oxy- 
gen, and  aldehyde  by  the  replacement  of  the  hydroxyl  group  and 
one  atom  of  hydrogen  by  an  atom  of  oxygen.  Water  is  of  course 
formed  in  both  cases. 

CH3-CH2.0H  f     0      =     CR3-CHO        +     H20 

Alcohol.  Aldehyde. 

CH3-CH2.OH  +     O2    =     CH3-CO.OH     +     H20 

Alcohol.  Acetic  acid. 

The  slow  oxidation  of  alcohol  may  be  made  to  develop  consid- 
erable heat.  Over  a  little  alcohol  in  a  beaker  we  suspend  a  coil 
of  platinum  wire  which  we  have  previously  heated  to  redness 


ALCOHOL.  195 

(Fig.  90).  The  wire  becomes  bright  red,  and  will  continue  to 
glow  as  long  as  sufficient  air  and  alcohol  vapor  come  in  contact 
with  it.  At  the  temperature  of  the  red-hot  wire 
the  alcohol  vapor  is  fully  oxidized,  but  if  we 
remove  it,  and  allow  it  to  cool  slightly,  and  then 
withdraw  it  before  it  becomes  bright,  we  may 
notice  the  peculiar  odor  developed  in  the  beaker. 
This  is  due  to  the  formation  of  aldehyde. 

To  test  for  alcohol  in  solution  we  add  a  flake 
or  two  of  iodine,  and  then  potassium  hydroxide  until  the  brown 
color  disappears.    A  yellow  precipitate  of  iodoform  results  if  alco- 
hol be  present.    The  smell  of  this  iodoform  is  very  characteristic. 

306.  The  reaction  of  alcohol  with  solutions  of  certain  metals  in  nitric  acid 
yields  a  class  of  bodies  called  the  fulminates.  Fulminating  mercury,  which  is 
used  for  charging  percussion-caps,  may  be  prepared  by  dissolving  about  two 
grammes  of  mercury  in  fifteen  cubic  centimetres  of  strong  nitric  acid  contained 
in  a  rather  large  flask  or  beaker.  The  reaction  is  aided  by  a  gentle  heat,  and 
as  soon  as  all  the  mercury  has  disappeared,  the  vessel  is  removed  from  the 
proximity  of  flame,  and  twenty  cubic  centimetres  of  alcohol  are  added.  A 
violent  reaction  takes  place,  dense,  white,  poisonous  vapors  are  disengaged, 
and  fulminate  of  mercury  is  deposited  as  a  light-gray  powder.  When  the 
effervescence  has  ceased,  the  vessel  is  filled  with  water,  and  the  acid  liquid  is 
poured  off" :  the  mercuric  fulminate  is  washed  by  decantation,  until  the  water 
no  longer  becomes  acid.  It  is  then  collected  on  a  small  filter,  and  dried  by 
exposure  to  the  air.  The  reaction  by  which  this  compound  is  formed  is  very 
complicated,  but  the  composition  of  mercuric  fulminate  is  expressed  by  the 
formula  HgC2N202,  and  its  molecule  is  believed  to  represent  methane,  CH*,  in 
which  the  hydrogen  is  replaced  by  NO2,  a  cyanogen  group,  and  mercury. 
CH*,  Methane.  C(N02)(CN)Hg,  Fulminate  of  mercury. 

Fulminate  of  mercury  explodes  violently  by  friction  or  percussion,  and  should 
be  kept  in  loosely- corked  bottles,  lest  it  be  exploded  by  the  friction  of  a  glass 
stopper.  It  explodes  also  at  a  temperature  of  about  180°.  Although  this  body 
is  so  exceedingly  explosive  that  it  would  burst  a  gun-barrel  in  which  it  was 
detonated,  the  expansive  force  of  the  gases  produced  is  much  inferior  to  that  of 
those  disengaged  by  gunpowder,  and  it  could  not  be  used  for  projectile  effects. 

307.  ALCOHOLIC  BEVERAGES  are  products  of  the  fermentation 
of  substances  containing  glucose  or  some  body  capable  of  being 
converted  into  glucose.  In  the  manufacture  of  wine,  the  glu- 
cose is  derived  from  the  juice  of  the  grape:  the  ferment  also 
is  natural  to  the  grape,  for  it  is  developed  from  the  albumen- 


196  LESSONS    IN    CHEMISTRY. 

like  matter  of  the  pulp.  Since  the  alcoholic  fermentation  is  a 
transformation  of  glucose,  and  no  air  is  necessary  for  the  change, 
this  fermentation  may  continue  in  closed  vessels ;  in  sparkling 
wines  or  champagnes  part  of  the  fermentation  takes  place  in  the 
bottle,  and  the  carbon  dioxide  formed  is  dissolved  in  the  liquid 
under  pressure.  All  the  carbon  dioxide  has  escaped  from  still 
wines.  The  fermentation  of  apple-juice  and  the  juices  of  other 
fruits,  which  yields  cider  and  the  various  fruit-wines,  is  quite 
similar  to  the  fermentation  of  grape-juice.  Wines  contain  from 
seven  to  twenty  per  cent,  of  alcohol. 

Beer,  ale,  and  porter  are  produced  from  grain,  preferably  from 
barley.  Grain  contains  no  glucose,  but  during  the  sprouting  of 
the  grain,  a  ferment,  diastase,  is  formed,  which  subsequently 
converts  the  starch  in  the  grain  into  a  sugar,  called  maltose. 
The  barley  is  moistened  and  kept  at  a  temperature  of  about  15° 
until  a  sprout  as  long  as  the  grain  is  formed.  The  sprouting  is 
then  arrested  by  heating  the  grain,  which  is  now  called  malt, 
to  about  50°,  after  which  it  is  ground  to  a  coarse  powder  and 
is  ready  for  brewing.  It  is  then  cooked  for  several  hours  with 
water  at  a  temperature  of  60°  :  maltose  is  produced,  and  this  as 
well  as  other  nutritious  matter  of  the  malt  is  dissolved.  The 
liquid  thus  formed  is  heated  with  hops  to  impart  an  aromatic 
flavor,  and  is  then  rapidly  cooled ;  after  a  little  yeast  is  added, 
the  wort  is  allowed  to  ferment  at  as  low  a  temperature  as  pos- 
sible, until  in  a  few  days  beer  or  ale  is  obtained,  according  to 
the  proportions  of  substances  used. 

Beer  contains  from  two  to  five  per  cent,  of  alcohol,  and  ale  a 
somewhat  larger  proportion,  sometimes  as  high  as  ten  per  cent. 
As  there  is  in  this  country  no  government  inspection  of  malted 
liquors,  beer  is  often  adulterated  by  the  substitution  of  various 
more  or  less  injurious  bitter  substances  for  the  hops,  and  of  glu- 
cose for  a  part  of  the  malt :  glucose  is  not  injurious,  but  it  con- 
tains no  nutritious  matter,  as  is  the  case  with  malt. 

SPIRITUOUS  LIQUORS  are  not  natural  products  ;  they  are  dis- 
tilled from  various  fermented  liquids,  and  are  only  dilute  alcohol 
containing  some  flavoring  matter.  Brandy  is  distilled  from  wine ; 
whiskey  from  malted  liquors  of  all  kinds,  derived  from  corn,  rye, 


ALCOHOLS.  197 

oats,  and  even  potatoes ;  rum  is  distilled  from  fermented  molasses 
from  sugar-cane  ;  gin  is  dilute  alcohol  flavored  with  the  essential 
oil  of  juniper-berries.  These  liquids  contain  from  forty  to  sixty 
per  cent,  of  alcohol. 


LESSON    XXXVIII. 
ALCOHOLS  (2). 

308.  Propyl  Alcohols,  C3H7.OH. — A  substance  of  this  com- 
position  exists  in  very  small  proportion  among  the  products  of  the 
alcoholic  fermentation.  It  is  a  liquid,  boiling  at  98°.  When  we 
examine  the  composition  of  the  hydrocarbon  propane,  we  will  no- 
tice that  the  three  carbon  atoms  are  not  similarly  related  :  two  are 
related  to  one  other  carbon  atom,  but  the  third  is  related  to  both 
of  the  first  two. 

HHH 
H-C-C-C-H 

HHH 

Chemists  have  discovered  two  propyl  alcohols,  and  indeed  two 
modifications  of  every  compound  containing  the  radical  propyl, 
C3H7.  We  account  for  this  in  our  theory  by  considering  that  in  one 
of  these  alcohols  the  hydroxyl  group  replaces  one  of  the  hydrogen 
atoms  of  either  of  the  two  carbon  atoms  which  are  related  to  only  one 
other  carbon  atom,  and  we  see  that  all  these  atoms  of  hydrogen  are 
similarly  situated.  The  alcohol  so  formed  is  normal  propyl  alcohol, 
that  which  we  have  briefly  considered.  In  the  other  alcohol  of 
the  same  composition  the  hydroxyl  group  is  joined  to  that  carbon 
atom  which  is  related  to  two  others :  it  is  called  isopropyl  alcohol, 
and  boils  at  81°.  We  see,  then,  that  there  are  two  propyl  radi- 
cals: propyl,  CH3-CH2-CH2;  and  isopropyl,  CH(CH3)2.  Those 
alcohols  in  which  the  carbon  atom  which  holds  the  hydroxyl  group 
in  the  molecule  is  related  to  only  one  other  atom  of  carbon,  are 
called  primary  alcohols.  Those  in  which  the  hydroxyl  group  is  in 


198  LESSONS   IN    CHEMISTRY. 

relations  with  an  atom  of  carbon  which  is  related  to  two  others, 
are  called  secondary  alcohols. 

309.  Butyl  Alcohols,  C4H9.OH.— Chemists  have  succeeded  in 
preparing  four  different  butyl  alcohols.    They  are  all  liquids,  with 
the  exception  of  one,  which  is  a  crystalline  solid,  in  whose  mole- 
cule we  believe  that  the  hydroxyl  group  is  held  by  a  carbon  atom 
which  acts  as  the  centre   of  a  system ;    around  this  atom  are 
grouped  three  other  atoms  of  carbon  and  their  accompanying  hy- 
drogen atoms.     It  is  C(CH3/OH.     It  is  called  a  tertiary  alcohol, 
that  being  the  name  applied  to  those  alcohols  in  which  the  carbon 
atom  which  brings  the  hydroxyl  group  into  the  molecule  is  related 
to  three  other  carbon  atoms. 

310.  Amyl  Alcohols,  C5HU.OH._ There  are  now  known  eight 
alcohols  of  this  composition.     Two  of  them  exist  in  the  oily  resi- 
due which  is  left  in  the  distillation  of  brandy  and  whiskey,  and 
they  are  therefore  products  of  the  alcoholic  fermentation  of  glu- 
cose.    This  oily  residue  is  called  fusel  oil :  it  has  a  peculiar  and 
not  altogether  pleasant  odor,  and,  besides   some  ordinary  alcohol 
which  it  still  retains,  is  a  mixture  of  propyl,  butyl,  and  two  amyl 
alcohols.     The  first  two  may  be  isolated  from  the  mixture  by 
careful  fractional  distillation,  but  for  the  separation  of  the  two 
amyl  alcohols  chemical  means  must  be  employed.      The  crude 
fusel  oil  is  a  valuable  solvent  for  many  substances,  to  dissolve 
which  ordinary  alcohol  would  otherwise  be  required.     Butyl  and 
amyl  alcohols  do  not  mix  in  all  proportions  with  water,  as  do  ethyl 
and  propyl  alcohols. 

We  pour  small  quantities  of  methyl,  ethyl,  butyl  alcohol  from 
fusel  oil,  and  amyl  alcohol  from  fusel  oil,  into  four  separate  plates, 
and  light  them.  We  find  that  the  first  is  the  most  combustible, 
and  that  we  can  light  the  last  only  with  difficulty.  The  flame  of 
the  methyl  alcohol  is  almost  colorless,  but  the  brightness  of  the 
flames  increases  to  the  amyl  alcohol,  which  burns  with  a  bright 
light.  The  effect  of  an  increased  number  of  carbon  atoms  com- 
bined in  the  molecule  is  then  to  render  the  compound  less  volatile, 
and  more  difficult  to  inflame. 

311.  Glycols. — We   have   learned   that  when   ethylene    gas, 


GLYCEROL.  199 

C2H4,  is  passed  into  bromine,  a  direct  combination  takes  place, 
and  ethylene  bromide,  C2H4Br2,  is  formed ;  we  have  also  acquired 
some  idea  of  the  molecule  of  this  new  compound.  When  ethylene 
bromide  is  boiled  with  a  solution  of  potassium  carbonate  in  water, 
carbon  dioxide  is  given  off,  and,  in  addition  to  the  potassium 
bromide  which  is  formed,  the  liquid  contains  a  new  body. 

C2H4Br2  +  R2C03  +  H2Q  =  C2H*(OH)2  +  2KBr  +  CQ2 
This  new  compound,  C2H4(OH)2,  is  formed  by  the  replacement 
of  the  two  bromine  atoms  of  ethylene  bromide  by  two  hydroxyl 
groups.  It  is  called  ethylene  alcohol,  and  after  the  potassium 
bromide  has  crystallized  it  can  be  separated  by  careful  fractional 
distillation,  and  then  forms  a  syrupy  liquid  having  a  sweet  taste. 
Since  it  is  a  neutral  body,  and  is  a  hydroxide,  it  is  called  an  alco- 
hol, and  it  is  a  diatomic  alcohol,  because  it  contains  two  hydroxyl 
groups.  It  is  the  first  member  of  a  series  of  diatomic  alcohols 
derived  from  the  hydrocarbons  of  the  series  CnH2n.  From  its 
sweet  taste,  Wurtz,  its  discoverer,  gave  it  the  name  glycol,  and  the 
diatomic  alcohols  are  often  called  glycols. 

312.  Glycerol,  or  Glycerin,  C3H3(OH)3.— The  fats  and  fatty 
oils  are  complex  compounds  containing  the  radicals  of  certain 
carbon  acids,  called  the  fatty  acids  (§  338),  and  the  radical  of  the 
well-known  substance  glycerol.  By  the  action  of  metallic  hydrox- 
ides on  these  compounds,  atoms  of  metal  replace  the  glycerol 
radical,  which  combines  with  the  hydroxyl  groups  which  were  be- 
fore in  the  metallic  hydroxide  molecules.  At  high  temperatures, 
steam  acts  precisely  like  the  metallic  hydroxides,  and  glycerol 
is  manufactured  by  distilling  fats  and  oils  in  a  current  of  super- 
heated steam  ;  that  is,  steam  which  has  been  passed  through 
very  hot  pipes.  The  radical  of  glycerol  having  been  found  to 
be  the  group  C3H5,  we  may  represent  the  change  thus : 

C3H5(fatty  acid  radical)3  +  3HOH  =  C3H5(OH)3  +   3H(fatty  acid  radical) 
Fat  or  Oil.  Water.  Glycerol.  Fatty  acid. 

Glycerol  is  a  colorless,  syrupy  liquid,  having  a  sweet  taste.  Its 
density  is  about  1.28.  It  freezes  below  0°,  and  melts  at  about 
17°.  When  it  is  heated,  it  boils  at  about  290°,  but  is  partially 
decomposed,  producing  a  very  irritating  odor  of  a  substance  called 


200  LESSONS  IN  CHEMISTRY. 

acrolein.     It  may  be  distilled  in  a  vacuum  or  in  a  current  of 
steam.     It  dissolves  in  all  proportions  of  water  and  alcohol. 

A  molecule  of  glycerol  contains  three  hydroxyl  groups  ;  gly- 
cerol  is  then  a  triatomic  alcohol.  Each  of  these  hydroxyl  groups 
may  be  replaced  by  a  monatomic  atom  or  radical,  and  a  large 
number  of  glycerol  derivatives  have  been  so  formed. 

313.  NITROGLYCERIN,  C3H5  (NO3)3.— In  a  little  beaker  glass 
placed  in  ice-water,  we  have  prepared  a  mixture  of  equal  volumes 
of  strong  sulphuric  and  nitric  acids ;  into  this  cold  mixture  we 
pour  a  few  drops  of  glycerol,  and,  after  stirring  for  a  few  moments, 
we  throw  the  contents  of  the  beaker  into  another  glass  nearly 
filled  with  cold  water.  A  few  drops  of  an  oily  liquid  separate, 
and  fall  to  the  bottom  of  the  glass ;  we  pour  off  nearly  all  the 
water ;  then,  by  means  of  a  glass  tube  drawn  out  to  a  small  open- 
ing, we  remove  a  drop  of  the  oil,  and  place  it  on  the  corner  of  a 
piece  of  paper  ;  when  we  light  this,  it  burns  with  a  bright  flash. 
We  now  allow  another  small  drop  to  fall  on  a  nearly  red-hot  piece 
of  sheet  iron  ;  it  explodes  with  a  loud  report.  We  place  another 
small  drop  on  an  anvil,  and  when  we  strike  it  with  a  hammer 
there  is  another  loud  explosion.  The  oil  is  nitroglycerin  ;  it  has 
been  formed  by  the  removal  of  three  molecules  of  water  from  one 
molecule  of  glycerol  and  three  molecules  of  nitric  acid,  and  the 
union  of  the  remaining  groups,  C3H5  and  3N03. 

C3H&(OH)3  +  3HNQ3  =  3H2Q  +  C3H5(N03)3 
When  nitroglycerin  explodes,  carbon  dioxide  and  water  are  formed. 
The  energy  of  the  explosion  is  due  to  the  energy  of  motion  of  the 
atoms  in  a  molecule  of  nitroglycerin  being  greater  than  that  en- 
ergy in  the  carbon  dioxide,  water,  and  nitrogen,  and  during  the 
explosion  the  excess  of  energy  appears  as  heat  and  the  energy 
necessary  to  convert  the  products  into  the  gaseous  state.  Nitro- 
glycerin is  used  in  blasting  operations,  but  it  is  usually  mixed  with 
a  very  fine  sandy  earth,  and  the  mixture  is  called  dynamite.  This 
is  made  into  cartridges  which  are  exploded  by  a  fuse  and  deto- 
nating cap(  Nitroglycerin  is  not  a  safe  body  to  handle ;  for  experi- 
mental purposes  we  prepare  only  a  few  drops  of  it,  and  it  is  better 
to  dry  the  compound  by  a  few  hours'  exposure  to  dry,  warm  air 
before  using  it. 


SIMPLE   ETHERS. 


201 


LESSON    XXXIX. 
SIMPLE  ETHERS. 

314.  Oxides  of  Hydrocarbon  Radicals.— In  a  glass  flask  we 
have  cautiously  mixed  some  methyl  alcohol 

with  about  its  own  volume  of  strong  sul- 
phuric acid;  after  adapting  a  cork  and 
straight  tube  to  the  flask,  we  heat  it,  and 
soon  a  colorless  gas  is  disengaged.  We 
light  the  gas,  and  it  burns  with  a  rather 
bright  flame.  (Fig.  91.)  It  is  methyl  ox- 
ide ;  the  sulphuric  acid  has  removed  a  mole- 
cule of  water  from  two  molecules  of  methyl 
alcohol,  and  the  two  methyl  groups  are  held 
together  by  an  atom  of  oxygen. 

2CH3.OH        =  (CH3)20          +  H20 

Methyl  alcohol.  Methyl  oxide. 

The  density  of  methyl  oxide  compared  to 
hydrogen  is  23.  The  gas  is  converted  into 
a  liquid  at  a  temperature  of  — 23°.  It  is 
soluble  in  water,  alcohol,  and  ether. 

In  this  compound  we  are  again  shown  that  the  methyl  group 
acts  like  an  atom  of  hydrogen.  It  is  a  monatomic  radical,  and  the 
composition  of  methyl  oxide  is  like  that  of  water,  excepting  that, 
instead  of  two  atoms  joined  by  an  atom  of  oxygen,  two  groups 
or  systems  are  held  to  the  oxygen  atom. 

H-O-H  H3C-0-CH3 

Water.  Methyl  oxide. 

The  other  monatomic  radicals  form  similar  oxides,  and  these 
oxides  form  part  of  a  large  class,  called  the  simple  ethers. 

315.  ETHYL   OXIDE,   (C2H5)20.— This  compound,  which  is 
commonly  called  ether,  may  be  formed  by  a  number  of  reactions. 
In  a  strong  glass  tube  we  have  sealed  some  ethyl  iodide  and  silver 


FIG.  91. 


202 


LESSONS    IN    CHEMISTRY. 


oxide,  and  have  heated  the  tube  for  several  hours  in  boiling  water. 
We  now  find  that  the  black  color  of  the  silver  oxide  has  changed 
to  yellow,  which  is  the  color  of  silver  iodide.  A  double  decom- 
position has  taken  place,  yielding  silver  iodide  and  ethyl  oxide, 
which  we  may  recognize  by  its  odor  and  other  properties  when  we 
cut  open  the  tube. 

Ag20        +        2C2H5I        -        2AgI        +        (C2H5)20 
Silver  oxide.          Ethyl  iodide.  Silver  iodide.  Ethyl  oxide. 

In  a  rather  large  flask  we  have  mixed  some  ninety  per  cent, 
alcohol  with  one  and  four-fifths  times  its  weight  of  strong  sulphuric 
acid.  We  adapt  to  this  flask  a  cork  having  three  holes  ;  through 
one  passes  a  thermometer  (2,  Fig.  92)  ;  another  gives  passage  to  a 


FIG.  92. 


tube  through  which  we  may  allow  alcohol  to  flow  from  a  reservoir, 
while  to  the  third  is  fitted  a  delivery-tube  connected  with  a  con- 
denser through  which  flows  a  stream  of  ice- water.  We  now  heat 
the  flask  until  the  thermometer  shows  that  the  liquid  into  which 


ETHYL   OXIDE.  203 

the  bulb  dips  has  a  temperature  of  140° ;  then  we  regulate  the 
flame  so  that  the  temperature  may  not  rise  further,  and  start  a 
small  stream  of  alcohol  from  the  reservoir.  This  alcohol  is 
quickly  changed  to  ether,  which,  together  with  the  water  formed, 
distils  and  collects  in  the  receiving-bottle. 

The  reaction  which  takes  place  in  this  operation  is  worth  our 
study.  When  alcohol  is  mixed  with  strong  sulphuric  acid,  water 
is  formed,  and  an  ethyl  group  is  substituted  for  one  atom  of  hy- 
drogen of  sulphuric  acid,  producing  a  compound  called  ethyl  sul- 
phuric acid. 

C2H5.0H     +    H2SO*    =    H20     +     (C2H»)HSO* 
Alcohol.  Ethylsulphuric  acid. 

If  this  ethyl  sulphuric  acid  is  heated,  it  is  converted  into  sul- 
phuric acid  and  ethylene  gas,  C2H* ;  if  it  is  boiled  with  water,  it 
again  yields  alcohol  and  sulphuric  acid ;  but  if  it  is  boiled  with 
an  additional  quantity  of  alcohol,  the  result  is  sulphuric  acid  and 
ether. 

(C2H5)HS04     +     C2H5.0H    =     H2SO*    +     (C?H5)20 
Ethylsulphuric  acid.         Alcohol.  Ether. 

If  methyl  alcohol  be  used  instead  of  ethyl  alcohol,  a  mixed  oxide 
of  methyl  and  ethyl  is  produced. 

(C2H5)HS04    +    CH3.OH    =     H2S04    +    CH3-0-C2H5 

Ethyl  oxide  is  a  colorless,  very  mobile  liquid,  having  a  pleasant 
odor  and  a  somewhat  burning  taste.  Its  density  at  0°  is  0.736  ; 
it  boils  at  34.5°.  It  will  dissolve  in  nine  times  its  weight  of  water, 
and  one  part  of  water  will  dissolve  in  thirty-six  parts  of  ether. 
Ether  dissolves  small  quantities  of  sulphur  and  phosphorus,  and 
large  proportions  of  bromine,  iodine,  fats,  oils,  and  many  other 
substances  which  are  insoluble  in  water. 

Ether  is  very  inflammable,  and  its  vapor  forms  an  explosive 
mixture  with  air.  We  suspend  a  heated  coil  of  platinum  wire 
over  a  little  ether  in  a  beaker,  as  we  made  a  similar  experiment  with 
alcohol,  and  the  slow  combustion  of  the  ether  vapor  develops  so 
much  heat  that  the  platinum  wire  becomes  hot  enough  to  inflame 
the  ether. 

The  vapor  of  ether  is  very  heavy, — 2.564  compared  to  air.    We 


204  LESSONS   IN   CHEMISTRY. 

pour  a  little  ether  into  a  warm  beaker,  and  then,  holding  the  short 
end  of  a  small  siphon  immediately  above  its  surface,  establish  a  cur- 
rent of  ether  vapor  by  drawing  out  the 
air  by  the  mouth ;  the  heavy  ether  vapor 
continues  to  flow  through  the  siphon,  as 
would  a  liquid,  and,  when  we  light  it,  will 
burn  as  long  as  any  ether  remains  in  the 
beaker  (Fig.  93). 

The  inhalation  of  ether  vapor  produces 
anaesthesia,   and   for   this  reason   ether  is 
largely  employed  as  an  anaesthetic  in  surgi- 
— 93  cal  operations. 

The  other  monatomic  hydrocarbon  radicals  form 

oxides  corresponding  to  the  oxides  of  methyl  and  ethyl :  each  of  these  con- 
tains two  radicals  related  to  one  atom  of  oxygen.  The  diatomic  hydrocarbons, 
ethylene  and  its  homologues,  form  oxides  containing  one  atom  of  oxygen  and 
one  molecule  of  the  hydrocarbon,  as  in  ethylene  oxide,  which  may  be  obtained 
by  heating  ethylene  bromide  with  silver  oxide. 


Ethylene  bromide.       Silver  oxide.        Ethylene  oxide.  Silver  bromide. 

316.  Chlorides,  Bromides,  etc,— The  class  of  simple  ethers 
includes  the  chlorides,  bromides,  iodides,  sulphides,  etc.  of  the 
radicals,  and  in  general  those  compounds  which  correspond  to  the 
simple  salts  of  the  metals, — that  is,  those  salts  formed  by  an  acid 
containing  no  oxygen. 

These  compounds  may  be  made  by  heating  together  the  corre- 
sponding acid  and  alcohol.  If  methyl  alcohol  is  heated  with 
strong  hydrochloric  acid,  a  colorless  gas,  methyl  chloride,  CH3C1, 
is  disengaged. 

317.  ETHYL  IODIDE,  C2H5I. — In  a  glass  flask  we  put  some 
alcohol  with  about  two-thirds  its  weight  of  amorphous  phospho- 
rus ;  to  this  flask  we  fit  a  cork,  through  which  passes  a  bottle- 
shaped   tube  called  an  adapter.     We  have  partially  closed  the 
lower  end  of  the  adapter  with  some  broken  glass,  and  on  this  have 
placed  a  mixture  of  broken  glass  with  a  quantity  of  iodine  equal 
to  two  and  three-fourths  times  the  weight  of  the  alcohol.     The 


ETHYL    IODIDE   AND   BROMIDE. 


205 


upper  end  of  the  adapter  is  connected  with  a  condenser  so  inclined 
that  liquid  may  flow  from  it  into  the  flask  (Fig.  94).     When  we 

heat  the  flask, 
the  alcohol 
boils,  and  its 
vapor,  conden- 
sing, runs  back 

through  the  iodine,  which  is  dissolved  and 
brought  gradually  in  contact  with  the  amor- 
phous phosphorus.  Phosphorus  tri-iodide, 
PI3,  is  then  formed ;  but  this  immediately 
reacts  with  the  alcohol,  forming  -ethyl  iodide 
and  phosphorous  acid.  The  whole  reaction 
is  expressed  in  the  equation 

3C2H5.0H  +  P  +  I3  =  3C2H5I     +     P(OH)3 
Alcohol.  Ethyl  iodide.  Phosphorous  acid. 

When  the  reaction  has  terminated,  we  agi- 
tate the  contents  of  the  flask  with  a  dilute  so- 
lution of  sodium  hydroxide,  and  decant  the 
aqueous  liquid  from  the  heavy  oily  layer  of 
ethyl  iodide.  We  then  remove  all  traces  of 
water  from  the  latter  by  shaking  it  with 
some  fragments  of  calcium  chloride,  and  may 
further  purify  it  by  fractional  distillation. 

Ethyl  iodide  is  a  colorless  liquid,  having 
at  0°  a  density  of  1.975.     It  boils  at  72°. 

318.  ETHYL  BROMIDE,  C2H5Br,  may  be  made  by  distilling  a 
mixture  of  alcohol,  potassium  bromide,  and  sulphuric  acid  diluted 
with  its  weight  of  water,  the  substances  being  used  in  the  pro- 
portions required  by  the  equation 

C2H5.0H     +     KBr     +     H2SO*    =     C2R5Br     +     KHSO4     +     H20 

It  is  a  liquid  having  a  pleasant  odor,  and  boiling  at  40°.  It  is 
sometimes  used  as  an  anesthetic. 

319.  By  various  means  the  hydrogen  atoms  of  these  simple  ethers  may  be 
replaced  by  chlorine,  bromine,  or  iodine,  and  compounds  are  then  formed 
which  we  may  consider  as  derived  from  other  radicals.  By  the  replacement 


FIG.  94. 


206  LESSONS    IN   CHEMISTRY. 

of  a  hydrogen  atom  in  ethyl  bromide  by  a  bromine  atom,  we  may  obtain 
either  ethylene  bromide,  CH2Br-CH2Br,  or  an  isomeric  compound  called 
ethylidene  bromide,  CH3-CHBr2.  One  of  the  more  important  of  the  sub- 
stances derived  by  the  continued  replacement  of  the  hydrogen  atoms  of  a 
simple  ether,  is  chloroform. 

320.  CHLOROFORM,  CHOP,  may  be  made  by  passing  methyl 
chloride  mixed  with  chlorine  over  charcoal  heated  to  about  200°. 
It  is  manufactured  by  distilling  a  mixture  of  alcohol  or  acetone 
with  chlorinated  lime,  commonly  called  bleaching  powder.     The 
reaction  is  very  complex.     Chloroform  and  water  condense  to- 
gether in  the  receiver,  and  the  choroform  separates  in  a  heavy  oily 
layer,  for  it  is  hardly  soluble  in  water.     It  is  decanted,  shaken 
first  with  water  and  then  with  a  solution  of  potassium  carbonate 
to  remove  impurities,  and  then  distilled  with  calcium  chloride, 
which  removes  the  little  water  which  it  held  in  solution. 

Chloroform  is  a  colorless  liquid  having  a  pleasant,  stimulating 
odor,  and  a  sweet,  burning  taste.  Its  density  is  1.5,  and  it  boils 
at  60.8.  It  is  not  inflammable,  and  communicates  a  green  tint 
to  a  flame  in  which  a  drop  of  it  is  introduced  on  the  end  of  a 
glass  rod.  It  is  used  as  an  anaesthetic. 

321.  There  is  a  bromoform,  CHBr3,  a  heavy,  colorless  liquid,  and  iodoform, 
CHI3,  a  yellow,  crystalline  solid.     They  are  formed  by  the  action  of  bromine 
and  iodine  on  alcohol  in  presence  of  alkalies.     Iodoform  is  used  in  surgery. 


LESSON    XL. 

ALDEHYDES,  CARBON  ACIDS,  AND   KETONES. 

322.  In  a  small  beaker,  we  mix  some  ordinary  alcohol  with  a 
little  potassium  dichromate  and  some  strong  sulphuric  acid.  The 
mixture  becomes  warm,  and  the  red  color  of  the  potassium  dichro- 
mate is  changed  to  green.  Potassium  dichromate,  a  compound 
derived  from  chromic  acid,  contains  much  oxygen,  and  it  is  re- 
duced by  the  alcohol,  which  becomes  oxidized.  The  peculiar  odor, 
somewhat  resembling  that  of  apples,  which  is  developed  in  the 


ALDEHYDE. — CHLORAL.  207 

beaker  glass,  is  due  principally  to  a  substance  called  aldehyde. 
Its  composition  is  C2H40,  and  it  represents  alcohol  in  which  the 
hydroxyl  and  one  hydrogen  atom  are  replaced  by  an  atom  of  oxy- 
gen. 

CH3-CH2.0H     +     0        =        CH3-CHO     +     H'O 
Alcohol.  Aldehyde. 

Aldehyde  is  made  by  distilling  a  mixture  of  alcohol,  sulphuric 
acid,  and  potassium  dichromate,  and  condensing  the  product  in  a 
receiver  surrounded  by  ice.  It  is  a  very  volatile  liquid,  boiling 
at  21°. 

323.  To  aldehyde  correspond  compounds  of  the  same  nature 
derived  from  each  primary  alcohol.    In  each  of  them  the  hydroxyl 
and  one  atom  of  hydrogen  of  the  corresponding  alcohol  are  re- 
placed by  an  atom  of  oxygen. 

324.  There  is  an  interesting  derivative  of  aldehyde  produced 
by  the  prolonged  action  of  chlorine  on  absolute  alcohol.     It  is  an 
oily  liquid,  called  chloral,  and  represents  aldehyde  in  which  three 
hydrogen  atoms  are  replaced  by  three  atoms  of  chlorine. 

CC13-CHO  CH3-CHO 

Chloral.  Aldehyde. 

Chloral,  or  trichloraldehyde,  combines  directly  with  water,  form- 
ing a  crystalline  compound  called  chloral  hydrate.  This  is  much 
used  in  medicine  for  its  sleep-producing  properties. 

325.  We  may  consider  that  an  aldehyde  is  an  oxidation  product 
of  an  alcohol.    If  the  oxidation  proceed  still  further,  the  aldehyde 
is  in  its  turn  converted  into  an  acid,  and  the  conversion  of  an 
alcohol  into  an  acid  may  take  place  without  the  previous  forma- 
tion of  an  aldehyde. 

Indeed,  a  carbon  acid  may  be  considered  as  a  primary  alcohol 
in  which  the  hydroxyl  remains,  but  the  two  atoms  of  hydrogen 
related  to  the  same  carbon  atom  as  the  hydroxyl  are  replaced  by 
an  atom  of  oxygen. 

CH3-CH2.OH     +     O3    =     CH3-CO.OH     +     H'O 

Alcohol.  Acetic  acid. 

We  consider,  then,  that  a  carbon  acid  is  a  compound  contain- 
ing the  monatomic  group  of  atoms  CO.OH,  and  this  group  is 
often  called  carboxyl.  As  in  all  acids,  the  hydrogen  of  the  hy- 


208  LESSONS    IN    CHEMISTRY. 

droxyl  group  may  be  replaced  by  metal,  and  salts  are  so  formed. 
If  there  be  only  one  carboxyl  group  in  the  acid,  there  can  be  only 
one  series  of  salts ;  but  if  there  be  two  carboxyl  groups,  we  can 
understand  that  either  both  or  only  one  of  the  hydrogen  atoms 
may  be  replaced,  and  there  will  be  two  series  of  salts,  neutral 
salts  and  acid  salts. 

326.  Formic  Acid,  HCO.OH,  is  the  acid  formed  by  the  oxi- 
dation of  methyl  alcohol.     We  have  already  seen  that  it  may  also 
be  produced  from  hydrocyanic  acid.    It  exists  naturally  in  certain 
insects,  and  it  takes  its  name  from  its  existence  in  ants.     It  is 
made  by  distilling  oxalic  acid  with  glycerol,  taking  care  that  the 
temperature  of  the  mixture  does  not  rise  above  110°.    The  oxalic 
acid  then  forms  with  the  glycerol  a  compound  which  is  again  de- 
composed when  more  oxalic  acid  is  added,  and  dilute  formic  acid 
distils,  while  the  glycerol  is  regenerated. 

C304H9        =        HCO.OH        -f-        C0a 
Oxalic  acid.  Formic  acid. 

Formic  acid  is  a  colorless,  very  acid  liquid,  having  a  pungent 
odor.  It  freezes  at  8.5°,  and  boils  at  100.8°.  It  mixes  with  water 
in  all  proportions.  To  a  little  formic  acid  in  a  test-tube,  we  add 
some  strong  sulphuric  acid,  and  gently  heat  the  tube :  an  effer- 
vescence takes  place,  and  we  may  light  the  escaping  gas  at  the 
mouth  of  the  tube.  It  is  carbon  monoxide,  for  the  formic  acid 
has  been  decomposed  into  that  gas  and  water. 
HCO.OH  =  CO  +  H20 

By  replacement  of  the  hydrogen  of  the  hydroxyl  in  formic  acid, 
formates  are  produced:  they  are  soluble  in  water,  and  yield  carbon 
monoxide  when  heated  with  sulphuric  acid. 

327.  Acetic  Acid,  C2H402  =  CH3-CO.OH,  is  obtained  in 
large  quantities  during  the  manufacture  of  charcoal  by  the  distilla- 
tion of  wood  in  closed  vessels  (§  226).     The  liquids  which  con- 
dense in  this  operation  consist  of  tarry  matter,  dilute  acetic  acid, 
wood-spirit,  and  some  other  substances.     After  the  tar  has  been 
separated,  the  acid  liquid  is  neutralized  with  lime,  and  a  crude 
calcium  acetate,  generally  called  pyrolignite  of  lime,  is  so  formed. 


ACETIC    ACID. 


209 


This  is  mixed  with  sodium  sulphate,  and  the  sodium  acetate  and 
insoluble  calcium  sulphate  formed  are  separated  by  filtration. 

Ca(C2H302)2        +        Na2SO*        =        CaSO*        +        2JTaC2H302 
Calcium  acetate.  Sodium  acetate. 

The  sodium  acetate  is  then  •  purified  by  crystallization,  and,  by 
heating  it  with  strong  sulphuric  acid,  is  again  converted  into 
sodium  sulphate  and  acetic  acid  which  distils. 

328.  Vinegar  is  a  dilute  acetic  acid  produced  by  the  oxidation 
of  alcohol.     The  oxidation  is  brought  about  by  a  minute  organ- 
ized ferment  which  has  the  property  of  absorbing  oxygen  from  the 
air  and  transferring  it  to  the  alcohol.     The  change  is  called  the 
acetic  fermentation  :  it  does  not  take  place  in  strong  alcohol.     In 
one  method  of  manufacture, 

the  dilute  alcohol,  or  wine,  is 
allowed  to  trickle  over  beech- 
wood  shavings  contained  in 
a  large  cask  having  a  double 
bottom  and  numerous  perfo- 
rations for  the  circulation  of 
air  (Fig.  95).  A  large  num- 
ber of  these  casks  are  placed 
in  rows,  and  the  shavings  are 
first  saturated  with  some  beet- 
juice  or  sour  wine  in  which 
the  ferment  is  already  devel- 
oped. The  slow  oxidation 
of  the  alcohol  produces  so 

much  heat  that  the  temper-  FIG.  95. 

ature  rises  to  30°.      It  is 

usually  necessary  to  allow  the  same  liquid  to  pass  twice  through 
the  cask  before  all  of  the  alcohol  is  changed  to  acetic  acid. 

329.  Pure  acetic  acid  is  a  corrosive  liquid,  having  a  pungent 
odor.     Its  density  at  0°  is  1.08;  it  freezes  at  17°,  and  boils  at 
118°.     It  is  soluble  in  all  proportions  of  water  and  alcohol. 

In  a  test-tube  we  neutralize  a  few  drops  of  acetic  acid  with  a 
fragment  of  solid  potassium  hydroxide  :  then  we  introduce  a  few 

14 


210  LESSONS    IN    CHEMISTRY. 

grains  of  arsenious  oxide,  and  heat  the  tube.  Dense  white 
vapors,  having  a  very  unpleasant  garlicky  odor,  are  disengaged. 
These  are  due  to  the  formation  of  a  very  poisonous  compound 
called  cacodyl.  The  test  enables  us  to  recognize  an  acetate. 

330.  Acetates.  —  Acetic  acid  contains  only  one  atom  of  hydrogen  replaceable 
by  metal,  and  the  acetates  must  contain  one  atom  of  a  metal  united  with  one 
of  more  groups,  C3H303,  according  to  the  atomicity  of  the  metal.     All  the 
acetates  of  the  metals  are  soluble  in  water. 

331.  SODIUM  ACETATE,  NaCaH3Oa  -f  3H30,  crystallizes  in  colorless  prisms, 
which  effloresce  in  dry  air,  and  the  water  may  be  entirely  driven  out  by  heat. 

332.  LEAD  ACETATE,  Pb(C2H302)2  +  3H20,  is  commonly  called  sugar  of  lead, 
owing  to  its  sweet  taste.     It  is  made  by  dissolving  lead  oxide,  PbO,  in  acetic 
acid.    Solutions  of  lead  acetate  are  capable  of  dissolving  an  excess  of  lead  oxide, 
and  when  carbon  dioxide  is  passed  through  the  liquid,  lead,  carbonate  is  precipi- 
tated, while  the  neutral  acetate  remains  in  solution.    Lead  acetate  is  poisonous. 

333.  COPPER  ACETATE,  Cu(C2H302)2  +  H20,  forms  beautiful  bluish-green 
crystals.     Verdigris  is  a  combination  of  copper  acetate  and  cupric  oxide,  CuO. 

334.  Acetone.  —  When  acetates  are  strongly  heated  they  are  converted  into 
carbonates,  and  a  vapor  is  given  off  which  may  be  condensed  to  a  liquid.    This 
has  the  composition  C3H60,  and  is  called  acetone. 

Ca(C2H302)3        =        CWO        +        CaCO3 


Acetone  is  found  among  the  products  of  the  dry  distillation  of  wood.  It  is 
a  colorless  liquid  of  peculiar,  not  unpleasant  odor.  It  boils  at  56.5°,  and  mixes 
with  water,  alcohol,  and  ether  in  all  proportions.  It  resembles  aldehyde  in  many 
of  its  reactions.  As  it  is  formed  when  isopropyl  alcohol,  CH3.CH(OH).CH3, 
is  oxidized,  we  write  its  formula  CH3.CO.CH3.  Analogous  compounds,  called 
ketones,  are  derived  from  other  secondary  alcohols. 

335.  Before  leaving  acetic  acid,  we  must  study  one  interesting  manner  of  its 
formation.     We  know  that  hydrochloric  acid  will  convert  hydrocyanic  acid 
into  formic  acid  ($  262),     If  the  hydrogen  of  hydrocyanic  acid  be  replaced 
by  a  methyl  group,  CH3,  methyl  cyanide  is  obtained,  CH3.CN  :  when  this  is 
treated  in  the  same  way,  acetic  acid  results. 

CH3CN        +        2H2Q        =        NH3        +        CH3COOH. 

The  higher  homologues  of  formic  and  acetic  acids  are  obtained  in  the  same 
way  from  the  corresponding  cyanides.  When  these  are  boiled  with  potassium 
hydroxide,  the  nitrogen  atom  is  always  changed  for  an  atom  of  oxygen  and 
the  group  OK,  thus  forming  a  salt  of  that  carbon  acid  which  contains  one  more 
carbon  atom  than  the  radical  of  the  cyanide. 

336.  The  general  formula  of  this  series  of  acids  is  CnH2n02.     The  higher 
members  form  part  of  the  natural  fats,  and  hence  the  series  is  generally  called 

'the  series  of  fatty  acids,    The  third  acid  is  propionic  acid,  C3H602,    There  are 


ETHEREAL    SALTS. 


211 


two  butyric  acids  :  one  of  them  exists  in  butter,  and  the  other  may  be  obtained 
from  isopropyl  cyanide.  There  are  three  valeric  acids,  C5H1002 ;  the  most 
common  exists  in  valerian  root.  It  is  a  colorless  liquid,  having  a  strong  and 
unpleasant  odor. 


LESSON    XLI. 
ETHEREAL  SALTS   AND  PATTY  ACIDS. 

337.  Ethereal    Salts. — In  a  glass  flask   connected. with  a 
good  condenser  (Fig.  96)  we  distil  a  mixture  of  strong  alcohol 


FIG.  96. 


with  nearly  twice  its  weight  of  strong  sulphuric  acid  and  three 
times  its  weight  of  crystallized  sodium  acetate.  A  colorless, 
volatile  liquid,  having  a  fragrant  odor,  condenses  in  the  receiver. 
This  body  is  ethyl  acetate,  and  has  been  formed  by  the  replace- 
ment of  the  sodium  atom  in  sodium  acetate  by  an  ethyl  group. 

NaC2H3Q2    +    C2R5.0H    +  I^SO*  =  C2H5.C2H3Q2   +  NaHSO*  +  H»0 
Sodium  acetate.  Ethyl  acetate. 

Ethyl  acetate  is  an  ethereal  salt  or  compound  ether,  and  may 
be  regarded  as  derived  from  acetic  acid  by  the  replacement  of 
its  basic  hydrogen  by  the  radical  ethyl.  Ethereal  salts  differ 


212  LESSONS   IN   CHEMISTRY. 

from  metallic  salts  in  that  they  contain  hydrocarbon  radicals 
instead  of  metallic  atoms ;  they  resemble  the  latter  in  the  man- 
ner in  which  they  are  formed,  as  well  as  in  their  ability  to  enter 
double  decompositions.  ThusT  ethyl  iodide  and  silver  nitrate  can 
be  made  to  react  and  produce  silver  iodide  and  ethyl  nitrate. 

C*H*I        +        AgXO*         =         Agl        +        C*H5.NO» 
BA|)lUMk  Sflrtr  mtnteu  SOrer  iodide.  Ethyl  nitnUe. 

We  gently  heat  some  ethyl  acetate  with  an  alcoholic  solution 
of  potassium  hydroxide ;  the  odor  of  the  ethyl  acetate  disap- 
pears ;  potassium  acetate  and  alcohol  have  been  formed. 
<7H*.C*H*0*    +     KOH     =     KCSH^O*    +    C*H*.OH 

338.  Many  of  those  ethereal  salts  in  which  both  basic  and 
acid  radical  are  carbon  compounds  exist  naturally  in  fruits, 
and  impart  to  these  their  characteristic  scents.     Amyl  acetate, 
C5HU.C1H3OS?  for  instance,  has  the  odor  of  pears,  and  methyl 
butyrate  and  amyl  valerate  exist  in  pineapples  and  apples. 
These  compounds  may  be  prepared   artificially  by  processes 
analogous  to  that  described  for  ethyl  acetate,  or  they  may  be 
made  by  passing  hydrochloric  acid  gas  through  a  mixture  of 
the  corresponding  acid  and  alcohol.     In  this  case  water  and  a 
simple  ether  (chloride)  are  first  formed,  and  the  latter  at  once 
reacts  with  the  carbon  acid,  the  result  being  a  compound  ether, 
while  hydrochloric  acid  is  regenerated. 

339.  Fatty  Acids. — As  the  number  of  carbon  atoms  in  the 
fatty  acids  increases,  these  substances  are  more  oily  in  nature  and 
less  soluble  in  water.    They  are  liquids  at  ordinary  temperatures 
until  the  molecule  contains  nine  atoms  of  carbon,  C*H18O* ;  the 
others  are  solids,  and  the  melting  point  is  higher  as  the  com- 
position is  more  complex.     Ethereal  salts  of  these  acids  exist 
in  various  vegetable  products  and  in  animal  secretions.     The 
peculiar  «dors  of  animals  are  due  to  fatty  acid  ethers.    We  must 
pass  by  the  intermediate  members  of  the  series  and  study  more 
particularly  those  which  are  most  largely  used  in  the  arts. 

340.  PALMITIC  ACID,  (P'IFH)*,  exists  in  palm  oil,  where  the 
radical  of  the  acid  is  combined  with  the  radical  C*H5  of  glycerol. 
It  is  manufactured  by  distilling  palm  oil  in  a  current  of  super- 


FATS  AND  OILS.  213 

heated  steam :  glycerol  and  palmitic  acid  are  formed,  and  the 
latter  solidifies  to  a  white  mass  on  cooling.  This  mass  is  strongly 
pressed,  to  remove  a  liquid  acid,  oleic  acid,  which,  existing  also  in 
a  glycerol  compound  in  the  palm  oil,  is  formed  at  the  same  time. 
The  palmitic  acid  is  then  used  for  the  manufacture  of  soap  and 
candles. 

341 .  STEARIC  ACID,  C^H^O1,  forms  a  large  proportion  of  tal- 
low, and  may  be  made  by  decomposing  that  substance  by  super- 
heated steam.     It  is  a  white  solid,  fusible  at  69°.     It  dissolves 
in  alcohol  and  ether,  and  may  be  crystallized  from  its  solutions. 
With  the  exception  of  the  alkaline  stearates,  the  salts  of  stearie 
acid  are  insoluble  in  water. 

342.  Oleic  Acid,  Cl*HS4O2.— Olive  oil  contains  the  glycerol 
compound  of  an  acid  which  does  not  belong  to  the  series  of  fatty 
acids.     It  is  an  unsaturated  carbon  compound,  and  its  molecule 
contains  two  atoms  of  hydrogen  less  than  that  of  stearie  acid.     It 
is  called  oleic  acid,  and  exists  in  many  oils  and  fids,  but  always 
mixed  with  certain  of  the  fatty  acid  compounds.     It  melts  at  14°, 
and  is  an  oily  liquid  at  ordinary  temperatures. 

343.  Fats  and  Oils.— The  natural  fats  and  fatty  oik  are  com- 
pound ethers  in  which  a  glycerol  radical  replaces  the  basic  hydro- 
gen of  the  fatty  acids.     We  have  already  seen  that  glycerol  is  a 
triatomic  alcohol :  it  contains  three  hydroxyl  groups,  and  in  the 
fats  and  oils  each  hydroxyl  group  is  replaced  by  a  fatty  add  less 
the  hydrogen  of  its  hydroxyl.     The  natural  fats  must,  then,  repre- 
sent three  molecules  of  fatty  acid  and  a  molecule  of  gljocwL 
The  names  of  these  fatty  bodies  are  derived  from  those  of  the 
fatty  acids  which  take  part  in  their  formation. 

344.  PALMITIN,  CsH5(C1*HaiO*/,  may  be  extracted  from  palm 
oil  which    has    been   solidified  by  cold   and   then   subjected   to 
pressure  to  remove  the  liquid  fatty  matters.     It  Is  a  white  solid, 
melting  at  60°. 

345.  STEARIN,  CsH5(CwH36Ofyj  is  also  solid ;  it  exists  in  the 
solid  fats,  such  as  tallow. 

346.  OLEIN,  C'H5(C18HS3O2)S,  constitutes  the  greater  portion 
of  olive  oil,  almond  oil,  and  other  analogous  oils.     It  is  a  liquid, 
which  solidifies  at  10°. 


214  LESSONS   IN   CHEMISTRY. 

Oils  are  usually  classed  as  fat  oils  and  drying  oils.  The  first 
are  such  as  do  not  solidify  on  exposure  to  air,  but  become  rancid 
and  acquire  an  unpleasant  odor.  They  are  numerous,  and  include 
olive  oil,  cotton-seed  oil,  oil  of  sweet  almonds,  peanut  oil,  and 
many  others.  The  drying  oils,  of  which  the  type  is  linseed  oil, 
absorb  oxygen  and  become  thick  and  hard  when  exposed  to  the 
air ;  they  are  used  in  the  preparation  of  paints  and  varnishes. 

347.  Saponification. — The  decomposition  of  a  compound 
ether  by  a  metallic  hydroxide,  a  decomposition  which  results  in 
the  formation  of  a  metallic  salt  and  an  alcohol,  is  in  chemical 
language  called  saponification ;  however,  a  more  restricted  sense 
of  the  word  implies  the  decomposition  of  a  fatty  body,  with  the 
formation  of  soap  and  glycerol.  We  boil  some  palm  oil  or  olive 
oil  with  a  solution  of  sodium  hydroxide  ;  the  oil  disappears,  and  a 
soap  has  been  formed,  while  glycerol  is  set  free  in  the  liquid.  It 
is  necessary  that  ordinary  soaps  shall  be  soluble  in  water,  and  we 
have  already  seen  that  the  only  ordinary  metals  which  yield  solu- 
ble salts  with  the  fatty  acids  are  potassium  and  sodium ;  in  other 
words,  the  alkaline  metals  (§  341).  Soap,  then,  is  an  alkaline  salt 
of  one  of  the  higher  fatty  acids,  generally  palmitic  and  stearic,  to 
which  must  be  added  oleic  acid.  Soft  soaps  are  made  with  potas- 
sium hydroxide,  while  sodium  hydroxide  yields  the  hard  soaps. 

In  the  manufacture  of  soap,  the  fat  or  oil  is  first  boiled  with 
a  rather  weak  solution  of  sodium  hydroxide,  generally  known  as 
concentrated  lye,  and,  when  the  mixture  becomes  pasty,  enough 
strong  caustic  soda  is  added  to  saponify  the  fat  completely.  To 
separate  the  excess  of  water,  common  salt  is  added  ;  this  dissolves 
in  the  water,  causing  the  soap  to  come  to  the  surface,  for  common 
soap  is  insoluble  in  salt  water.  The  salty  water,  containing  the  ex- 
cess of  alkaline  hydroxide  employed,  is  then  drawn  off,  and  the  soap 
hardens  on  cooling.  As  it  is  not  easy  to  separate  from  the  waste 
liquid  the  glycerol  formed  in  the  reaction,  it  is  more  economical  to 
decompose  the  fat  by  superheated  steam,  and  boil  with  sodium  hy- 
droxide the  fatty  acid  which  floats  on  the  dilute  glycerol.  While 
soap  is  soluble  in  water,  it  is  decomposed  by  a  large  quantity  of  that 
liquid,  a  small  quantity  of  alkaline  hydroxide  being  set  free,  while 


SAPONIFICATION.  215 

the  fatty  acid  becomes  insoluble.  The  free  alkali  produces  the 
cleansing  effects,  and  the  fatty  acid  forms  the  lather  :  we  know 
that  soap  will  not  produce  a  lather  if  we  use  too  little  water. 
Ordinary  soap  is  insoluble  in  salt  water,  but  a  soap  which  is  sol- 
uble in  salt  water  may  be  made  from  cocoanut  oil  ;  it  is  called  salt- 
water soap.  It  contains  an  alkaline  laurate  and  myristate,  lauric 
acid,  C12H2402,  and  myristic  acid,  C14H2802,  existing  as  glycerol 
ethers  in  cocoanut  oil. 

348.  STEARIN  CANDLES  are  made  from  a  mixture  of  solid 
fatty  acids  obtained  by  saponifying  tallow  by  superheated  steam 
and  a  small  quantity  of  lime.  The  small  quantity  of  insoluble 
calcium  soap  so  formed  is  decomposed  by  sulphuric  acid,  and  the 
oleic  acid  is  separated  from  the  solid  acids  by  pressing  the  mass 
between  warm  plates.  The  oleic  acid  is  used  for  the  manufacture 
of  soap.  Certain  fatty  bodies,  among  them  palm  oil,  are  entirely 
decomposed  by  superheated  steam,  without  the  aid  of  lime.  In 
this  reaction  the  water  acts  as  would  either  an  acid  or  an  alkaline 
hydrate,  part  of  its  molecule  completing  the  basic  molecule  of 
glycerol,  while  the  other  part  completes  the  acid  molecule. 


+     3HOH    -     C8H5(OH)3     + 
Palmitin.  Glycerol.  Palmitic  acid. 

The  saponification  of  fats  and  oils  may  be  brought  about  by  the 
action  of  strong  acids,  such  as  sulphuric  acid,  for  the  strong  acid 
forms  a  new  compound  ether  with  the  glycerol  radical,  and  sets 
the  fatty  acid  free  ;  the  compound  ether  may  then  be  again 
decomposed  into  glycerol  and  acid  by  the  addition  of  water. 


216  LESSONS    IN    CHEMISTRY. 

LESSON    XLII. 

CARBON  ACIDS   (3). 

349.  Lactic  Acid,  C3H6033  occurs  in  sour  milk,  and  is  pro- 
duced in  the  lactic  fermentation  of  various  sugars.     It  is  usually 
made  by  allowing  a  solution  of  glucose  to  which  some  sour  milk, 
a  little  old  cheese,  and  some  chalk  have  been  added,  to  ferment 
in  a  warm  place  until  the  whole  is  converted  into  a  solid  mass 
of  calcium  lactate.     This  is  purified  by  crystallization,  and  de- 
composed by  the  exact  quantity  of  sulphuric  acid  required  to 
precipitate  the  calcium  as  calcium  sulphate.     The  solution  is 
then   separated   by   a  filter,  and   evaporated  on  a  water-bath. 
Lactic  acid  remains  as  a  colorless,  very  sour,  syrupy  liquid,  which 
is  decomposed  when  heated. 

Lactic  acid  is  propionic  acid,  C3H60!,  in  which  one  atom  of  hydrogen  is 
replaced  by  a  hydroxyl  group ;  it  is  consequently  at  the  same  time  an  alcohol 
and  an  acid.  Chemists  have  obtained  another  acid  of  the  same  composition, 
an  isomeride  of  lactic  acid,  and  the  differences  of  the  two  are  due  to  different 
positionsof  the  hydroxyl  group.  The  isomer  is  called  hydracrylic  acid,  because 
it  is  decomposed  by  heat  into  water  and  an  acid  called  acrylic  acid,  C3H402. 

CH3-CH2-CO.OH  CH3-CH(OH)-CO.OH  CH2(OH)-CH2-CO.OH 

Propionic  acid.  Lactic  acid.  Hydracrylic  acid. 

Lactic  acid  exists  in  three  modifications  which  differ  from  one  another  in 
certain  physical  properties,  but  have  identical  molecular  structure.  (See 
Stereochemistry,  p.  346.) 

350.  Oxalic  Acid,   C2H204,  exists  naturally  in  many  plants ; 
it  gives  the  sour  taste  to  sour  grass,  and  at  certain  seasons  is 
present  in  small  quantities  in  rhubarb-leaves.     It  is  a  product  of 
the  oxidation  of  many  vegetable   matters:  it  may  be  made  by 
boiling  starch  with  rather  dilute  nitric  acid,  and  evaporating  the 
liquid.     It  is  now  manufactured  by  heating  to  200°  a  pasty  mix- 
ture of  saw-dust  and  potassium  hydroxide ;  potassium  oxalate  is  so 
formed,  and  is  separated  by  treating  the  mass  with  hot  water,  in 
which  it  is  quite  soluble.     The  solution  of  potassium  oxalate  is 


OXALIC   ACID.  217 

then  mixed  with  milk  of  lime,  which  is  calcium  hydroxide,  and 
insoluble  calcium  oxalate  is  formed,  while  the  solution  contains 
potassium  hydroxide,  which  is  used  for  another  operation. 

K2C20*  +  Ca(OH)2  =  CaC20*        +        2KOH 

Potassium  oxalate.  Calcium  hydroxide.  Calcium  oxalate. 

The  calcium  oxalate  is  decomposed  by  sulphuric  acid,  which 
forms  insoluble  calcium  sulphate,  and  the  solution  of  oxalic  acid  is 
evaporated  until  it  is  strong  enough  to  crystallize. 

Oxalic  acid  forms  large,  colorless  prisms,  containing  two  mole- 
cules of  water  of  crystallization.  In  dry  air,  these  crystals  efflo- 
resce, and  the  anhydrous  acid  may  be  obtained  by  carefully  heating 
them  to  100°.  Oxalic  acid  dissolves  in  fifteen  times  its  weight 
of  cold  water,  and  is  also  soluble  in  alcohol.  When  heated  to  about 
150°,  it  is  decomposed  with  formation  of  carbon  monoxide,  carbon 
dioxide,  formic  acid,  and  water. 

2C2H2Q*  CO        +        2CQ2        +        CH202        +        H*0 

Oxalic  acid.  Formic  acid. 

We  have  already  learned  that  both  carbon  monoxide  and  formic 
acid  are  prepared  by  the  decomposition  of  oxalic  acid. 

351.  We  neutralize  a  solution  of  oxalic  acid  by  the  addition  of 
a  little  ammonia-  water,  and  then  pour  into  it  some  solution  of 
calcium  chloride.  A  white  precipitate  of  insoluble  calcium  oxalate 
is  formed. 

(NH*)2C204        +  CaCl2  =          2NH*C1  -f        CaC20* 

Ammonium  oxalate.        Calcium  chloride.        Ammonium  chloride.       Calcium  oxalate. 

Oxalic  acid  is  poisonous  ;  its  antidote  is  chalk,  which  is  calcium 
carbonate  :  this  causes  the  formation  of  insoluble  calcium  oxalate. 

We  have  prepared  some  silver  oxalate  by  adding  solution  of 
silver  nitrate  to  a  solution  of  oxalic  acid  neutralized  with  ammonia. 
The  insoluble  silver  oxalate  is  separated  by  filtration  and  dried. 
When  we  heat  a  small  quantity  of  this  powder  in  a  test-tube,  it 
suddenly  explodes,  being  decomposed  into  carbon  monoxide,  carbon 
dioxide,  and  silver. 

Oxalic  acid  consists  of  two  carboxyl  groups,  and  is  therefore  a  dibasic  acid, 


i  With  monatomic  metals  it  may  form  two  series  of  salts,  acid  oxalates, 

CO.OH. 

in  which  only  one  atom  of  hydrogen  is  replaced  by  metal,  and  neutral  salts,  in 


218  LESSONS   IN   CHEMISTRY. 

which  both  atoms  are  so  replaced.     One  atom  of  a  diatomic  metal  like  calcium 
•will  of  course  replace  both  hydrogen  atoms. 

With  the  exception  of  the  oxalates  of  potassium,  sodium,  and  ammonium, 
the  neutral  oxalates  of  the  metals  are  insoluble  in  water,  but  they  are  decom- 
posed by  dilute  sulphuric  ami  hydrochloric  acids. 

352.  Tartaric  Acid,  C*H606,  is  the  acid  of  grapes.  In  the 
casks  in  which  wine  is  kept  there  is  deposited  an  impure  potas- 
siujn  acid  tartrate,  called  argol.  This  is  purified  by  crystallization 
from  boiling  water,  and  the  product  so  obtained  constitutes  cream 
of  tartar.  By  boiling  the  aqueous  solution  with  chalk,  and  add- 
ing sufficient  calcium  chloride  to  form  potassium  chloride  with 
the  potassium,  insoluble  calcium  tartrate  is  formed,  while  carbon 
dioxide  is  given  off,  and  potassium  chloride  remains  in  solution. 
The  calcium  tartrate  is  separated  by  filtration,  and,  after  being 
washed  with  water,  is  decomposed  with  the  theoretical  quantity 
of  dilute  sulphuric  acid.  Calcium  sulphate  is  precipitated,  and 
when  the  filtered  solution  has  been  sufficiently  concentrated  by 
evaporation,  crystals  of  tartaric  acid  are  formed. 

Tartaric  acid  is  in  large,  prismatic  crystals,  soluble  in  about 
half  their  weight  of  cold  water,  and  also  soluble  in  alcohol.  By 
the  action  of  heat  it  is  converted  into  several  other  acids,  of  which 
the  compositions  depend  on  the  temperature  at  which  the  tartaric 
acid  is  decomposed. 

353.  We  can  easily  understand  the  molecular  constitution  of  tartaric  acid 
by  studying  that  of  substances  to  which  it  is  intimately  related.  When  ethy- 
lene  cyanide  (CN)CH2-CH2(CN)  is  boiled  with  potassium  hydroxide,  ammonia 
is  disengaged,  and  there  is  formed  the  potassium  salt  of  auccinic  acid,  so  called 
because  it  is  formed  by  the  action  of  heat  on  amber. 

CH2-CN  CH2-CO.OH        +        2NHS 

CH2-CN       +     4H2°  CH2-CO.OH 

Ethylene  cyanide.  Succimc  acid. 

There  exists  in  apples,  gooseberries,  and  many  other  fruits  an  acid  called 
malic  acid,  and  this  has  also  been  prepared  artificially  in  such  a  manner  as  to 
show  that  it  represents  succinic  acid  in  which  one  atom  of  hydrogen  is  replaced 
by  a  hydroxyl  group.  The  replacement  of  two  hydrogen  atoms  of  succinic 
acid  by  hydroxyl  groups  yields  tartaric  acid. 

CH2-CO.OH  CH(OH)-CO.OH  CH(OH)-CO.OH 

CHZ-CO.OH  CH2-CO.OH  CH(OH)-CO.OH 

Succinic  acid.  Malic  acid.  Tartaric  acid. 


CITRIC   ACID.  219 

Tartaric  acid  is,  then,  a  diatomic  alcohol,  for  it  contains  two  hydroxyl  groups 
related  to  two  carbon  atoms,  and  it  is  a  dibasic  acid,  for  it  contains  two  car- 
boxyl  groups,  CO.OH.  There  are  two  series  of  tartrates,  acid  tartrates,  in  which 
only  one  atom  of  basic  hydrogen  is  replaced,  and  neutral  tartrates,  in  which 
both  are  replaced. 

Like  lactic  acid,  tartaric  acid  exists  in  several  modifications  differing  in 
certain  physical  properties.  (See  Stereochemistry,  p.  346.) 

354.  POTASSIUM   ACID  TARTRATE,   KC4H606,  is  cream  of 
tartar,  and  is  made  by  purifying  argol.     It  is  almost  insoluble 
in  cold  water,  but  dissolves  in  boiling  water.     When  heated  to 
redness,  it  leaves  a  residue  of  charcoal  and  potassium  carbonate, 
which  may  be  dissolved  from  the  mass  by  water.     Pure  potas- 
sium carbonate  is  usually  obtained  in  this  manner. 

355.  POTASSIUM  TARTRATE,  K2C4H406,  is  made  by  adding 
potassium  carbonate  to  a  boiling  solution  of  cream  of  tartar  as 
long  as  carbon  dioxide  is  disengaged.     When  the  concentrated 
solution  cools,  the  salt  separates  in  crystals  which  are  very  soluble 
in  water. 

356.  POTASSIUM  SODIUM  TARTRATE,  KNaC4H406,  is  com- 
monly called  Rochelle  salt.    It  is  made  by  neutralizing  with  so- 
dium carbonate  a  boiling  solution  of  cream  of  tartar.     It  forms 
beautiful,  colorless  crystals,  freely  soluble  in  water. 

357.  POTASSIUM   ANTIMONYL  TARTRATE,   K(SbO)C4H406, 
known  as  tartar  emetic,  is  formed  when  antimonous  oxide  is  boiled 
with  cream  of  tartar.     Its  crystals  contain  one  molecule  of  water 
of  crystallization  for  every  two  molecules  of  the  salt,  and  effloresce 
in  dry  air.     It  is  soluble  in  water,  and  is  poisonous.     When  hy- 
drogen sulphide  is  passed  through  its  solution,  an  orange-colored 
precipitate  of  antimony  sulphide  is  formed. 

358.  Citric  Acid,  C6H807,  exists  in  lemons,  oranges,  currants, 
and  many  other  fruits.      It  is  made  by  allowing  the  juice  of 
lemons  or  sour  oranges  to  stand  until  it  begins  to  ferment,  and 
then  neutralizing  the  boiling  filtered  liquid  with  chalk.     The  in- 
soluble calcium  citrate  formed  is  washed  with  boiling  water,  and 
decomposed  by  dilute  sulphuric  acid  ;  citric  acid  crystallizes  from 
the  solution  separated  from  the  insoluble  calcium  sulphate. 

Citric  acid  forms  large  colorless  crystals,  soluble  in  about  three- 


220  LESSONS    IN   CHEMISTRY. 

fourths  their  weight  of  cold  water,  and  having  a  very  sour  taste. 
Its  cold  solutions  are  not  precipitated  by  lime-water,  but  become 
turbid  when  the  liquid  is  boiled,  for  calcium  citrate  is  more 
soluble  in  cold  than  in  hot  water.  Magnesium  citrate  is  em- 
ployed as  a  purgative  in  medicine. 

Citric  acid  is  a  tribasic  acid  and  a  monatomic  alcohol :  its  molecular  struc- 
ture is  represented  by  the  formula 

CH2.COOH 

C(OH).COOH 
CH'.COOH 


LESSON  XLIII. 
CARBOHYDRATES. 

359.  The  principal  constituents  of  plants  are  substances  com- 
posed of  carbon,  hydrogen,  and  oxygen,  the  last  two  elements 
being  present  in  exactly  the  proportions  required  for  the  forma- 
tion of  water.     For  this  reason  they  have  been  called  carbo- 
hydrates, or  hydrates  of  carbon.     It  should  be  remarked,  how- 
ever, that   certain   compounds,  recently    discovered,*    contain 
different  proportions  of  hydrogen  and  oxygen,  although  they 
present  all  the  other  characteristics  of  this  class,  and  must  be 
included  in  it.    According  to  their  compositions  we  may  arrange 
the  carbohydrates  in  three  series,  of  which  glucose,  saccharose, 
and  starch  may  be  regarded  as  the  types. 

Of  the  very  numerous  substances  belonging  to  each  of  these 
series  we  can  study  but  a  few  of  the  more  common. 

360.  Glucose,  or  Dextrose,  C6H1206,  is  the  sugar  of  grapes, 
and  constitutes  the  efflorescences  seen  on  raisins  and  dried  figs. 
It  is  generally  associated  with  another  sugar,  fructose,  having 
the  same  composition.     Honey  and  the  juice  of  many  fruits  owe 
their  sweetness  to  a  mixture  of  these  sugars. 

*  For  example,  rhamnose,  which  has  the  composition  C6HI205. 


FRUCTOSE   OR   LEVULOSE.  221 

Glucose  is  manufactured  by  boiling  starch  with  a  large  quantity  of  water 
containing  about  one-half  per  cent,  of  sulphuric  acid.  The  starch  is  not  added 
until  the  liquid  is  boiling,  and  after  about  half  an  hour's  cooking  it  is  com- 
pletely converted  into  glucose.  The  sulphuric  acid  is  then  neutralized  with 
chalk,  and  after  the  insoluble  calcium  sulphate  has  been  separated  by  nitra- 
tion, the  solution  of  glucose  is  concentrated  until  it  will  solidify  to  a  crystalline 
mass  on  cooling. 

Glucose  forms  small,  rounded,  crystalline  masses,  which  con- 
tain one  molecule  of  water  of  crystallization  for  each  molecule 
of  glucose.  When  cautiously  heated,  it  melts,  and  again  be- 
comes solid  at  100°,  all  the  water  of  crystallization  heing  then 
expelled.  Glucose  dissolves  in  about  its  own  weight  of  cold 
water,  and  the  solution  has  a  sweet  taste.  It  is  much  employed 
in  confectionery  and  syrups,  but  it  is  only  about  one-third  as 
sweet  as  ordinary  sugar. 

In  a  test-tube  we  boil  a  mixture  of  sodium  hydroxide  solution, 
potassium  and  sodium  tartrate,  and  cupric  sulphate :  the  result- 
ing deep-blue  solution,  known  as  FMings  solution,  is  not  changed 
by  heat,  but  when  we  add  a  little  glucose  to  the  boiling  liquid, 
the  color  changes  to  yellowish  red,  and  on  standing  red  cuprous 
oxide  is  deposited.  The  glucose  has  reduced  the  cupric  solution : 
glucose  then  acts  as  a  reducing  agent.  To  a  solution  of  silver 
nitrate  we  add  ammonia  water  until  the  precipitate  at  first  formed 
is  just  redissolved.  Now  on  adding  a  little  glucose  and  gently 
warming  the  tube  a  brilliant  mirror  of  silver  is  formed  on  its 
walls.  In  these  reactions  the  glucose  is  oxidized  and  converted 
into  complex  acids. 

We  already  know  that  by  fermentation  glucose  is  decomposed 
into  carbon  dioxide  and  alcohol. 

361.  Fructose,  or  Levulose,  has  the  same  composition  as 
glucose,  and  resembles  it  in  most  of  its  properties.  It  is  more 
soluble  in  water  and  alcohol  than  the  latter,  melts  at  95°,  and 
rotates  the  plane  of  polarized  light  to  the  left,  while  glucose 
turns  it  to  the  right. 

The  glucose  molecule  contains  an  aldehyde  group,  CHO,  and 
five  hydroxyl  groups ;  that  of  fructose  a  carbonyl  group,  CO, 
and  five  hydroxyl  groups.  Both  sugars  are  monosaccharides : 


222  LESSONS    IN   CHEMISTRY. 

the  former  is  an  aldehyde-alcohol,  or  aldose,  the  latter  a  ketone- 
alcohol,  or  ketose.  They  have  recently  been  made  by  synthesis. 
362.  Saccharose,  or  Cane-Sugar,  C"HM0U.— This  com- 
pound,  which  is  ordinary  sugar,  is  extracted  principally  from 
sugar-cane,  sugar-maple,  beet-root,  and  sorghum. 

Maple-sugar  flows  from  incisions  made  in  the  bark  of  the  maple.  Sugar- 
cane, beet-root,  or  the  plants  from  which  sugar  is  to  be  extracted,  are  finely 
cut,  and  subjected  to  strong  pressure,  by  which  the  juice  is  expressed.  The 
liquid  is  then  heated  by  steam  in  large  boilers,  and  milk  of  lime  (calcium 
hydroxide)  is  added  to  neutralize  the  natural  acids  of  the  juice  and  form  in- 
soluble compounds  with  certain  nitrogenized  principles  which  are  present. 
The  dissolved  lime  is  precipitated  by  a  current  of  carbon  dioxide.  The  syrup 
is  then  heated,  and  filtered  through  a  layer  of  grained  animal  charcoal,  and 
afterwards  concentrated  at  as  low  a  temperature  as  possible  by  boiling  in  large 
vessels  in  which  a  vacuum  is  made  by  pumps.  When  sufficiently  concentrated, 
the  syrup  is  run  into  cooling-pans,  where  it  is  continually  stirred,  so  that  the 
sugar  may  separate  in  small  crystals,  as  granulated  sugar.  This  is  refined  by 
being  again  dissolved  and  filtered  through  animal  charcoal,  after  which  the 
syrup  must  be  again  evaporated  and  crystallized.  The  granulated  sugar  is 
freed  from  syrup  by  rapid  rotation  in  a  cylinder  of  wire  gauze,  through  which 
the  syrup  is  thrown  by  centrifugal  force.  The  still  moist  product,  called  soft 
sugar,  is  dried  by  being  sifted  on  a  revolving  cylinder  heated  by  steam  and 
contained  in  a  large,  partially  open  drum  through  which  a  current  of  air  is 
constantly  passing. 

The  dark-colored  mother  liquor  from  which  the  sugar  crystals  have  been 
separated  constitutes  molasses  or  treacle,  and  still  contains  about  50  per  cent, 
of  sugar.  This  sugar  may  be  extracted  by  converting  it  into  an  insoluble 
compound  (strontium  saccharate),  and  decomposing  the  latter  by  carbon 
dioxide. 

Sugar  is  insoluble  in  ether  and  in  absolute  alcohol.  Its  crystals 
are  anhydrous.  It  melts  at  160°,  and  on  cooling  forms  a  hard, 
amorphous  mass.  At  about  210°  it  is  partially  decomposed, 
yielding  a  brown,  bitter  substance  known  as  caramel.  It  does 
not  reduce  Fehling's  solution,  but  by  long  boiling  is  converted 
into  glucose,  which  then  effects  the  reduction. 

Solutions  of  cane  sugar  turn  the  plane  of  polarized  light  to 
the  right,  and  this  fact  is  taken  advantage  of  to  estimate  the 
amount  of  sugar  in  a  solution. 

Upon  warming  with  dilute  acids,  sugar  solutions  are  inverted  ; 
that  is,  they  will  rotate  the  plane  of  polarization  to  the  left. 


STARCH.  223 

This  is  due  to  the  fact  that  the  saccharose  molecule  is  resolved 
into  one  of  glucose  and  one  of  fructose,  and  the  latter  deflects 
the  plane  of  polarization  to  a  greater  extent  than  the  former. 


C12H22QH     +      H20      =      C6H1206      + 
Saccharose.  Glucose.  Fructose. 

Cane  sugar  represents  the  disaccharides,  to  which  also  belong 
its  isomers  maltose  and  lactose. 

363.  Lactose  is  a  hard,  not  very  sweet  substance  which  exists 
in  the  milk  of  animals,  and  is  usually  made  by  simply  evaporating 
the  whey  left  in  the  manufacture  of  cheese.     It  has  the  same 
composition  as  saccharose,  but  its  crystals  contain  one  molecule 
of  water  of  crystallization  to  one  of  lactose,  C12H22O*U  -f-  H'O. 
It  rotates  the  plane  of  polarization  to  the  right.     By  boiling 
with  dilute  acids  it  yields  glucose  and  its  isomer,  galactose. 

364.  Starch  is  found  everywhere  in  the  vegetable  kingdom, 
and  constitutes  the  greater  part  of  all  grains,  and  of  many  tube- 
rous roots  like  the  potato.     It  is  obtained  by  reducing  potatoes  to 
a  pulp,  and  washing  this  pulp  in  a  sieve  through  which  flows  a 
stream  of  water.    The  fibrous  matters,  consisting  of  the  torn  cells 
of  the  potato,  remain  in  the  sieve,  while  the  small  particles  of 
starch  pass  through  and  are  deposited  from  the  water,  which  is 
allowed  to  flow  slowly  down  long  inclined  planes.     From  grains 
the  starch  is  extracted  by  grinding  the  grain  to  flour,  and  knead- 
ing the  flour  in  a  sieve  under  running  water.     The  starch  passes 
through,  as  before,  while  the  nitrogenized  matter  of  the  grain 
forms  a  soft,  elastic  mass,  called  gluten. 

The  starch  so  obtained  is  simply  separated  from  the  vegetable 
cells  in  which  it  was  formed.  It  occurs  as  a  fine  powder,  in  which 
microscopic  examination  reveals  a  peculiar  granular  structure. 
The  size  and  shape  of  these  granules  vary  with  the  source  of  the 
starch  (Fig.  97)  :  they  are  from  2  to  185  thousandths  of  a  millimetre 
in  diameter.  They  are  formed  of  concentric  layers,  and  their 
structure  becomes  apparent  when  a  little  starch  is  dried  at  100°, 
and,  after  moistening  with  a  drop  of  water  containing  a  trace  of 
iodine,  is  examined  by  the  aid  of  a  microscope.  The  granules 


224 


LESSONS    IN    CHEMISTRY. 


then  swell,  and,  as  the  exterior  layers  burst,  the  interior  structure 
is  exposed  (Fig.  98). 

Starch  is  insoluble  in  water  and  alcohol ;  but,  when  it  is  rubbed 
with  water  in  a  mortar  with  rough  sides,  a  small  quantity  of  the 


FIG.  97. 


FIG.  98. 


interior  of  the  granules  appears  to  dissolve.  When  it  is  boiled 
with  a  large  quantity  of  water,  the  granules  burst,  and  a  turbid 
liquid  is  obtained  on  cooling  ;  this  contains  some  soluble  starch, 
and  holds  in  suspension  the  insoluble  starch.  When  heated  with 
water  to  60°  or  70°,  starch  forms  a  gelatinous  mass,  called  starch 
paste.  We  have  already  seen  that  starch  develops  a  blue  color 
with  iodine  ;  and  as  starch  is  the  test  for  iodine,  so  iodine  is  the 
test  for  starch.  The  blue  color  fades  on  heating. 

While  the  composition  of  starch  is  represented  by  the  formula 
C6H1005,  there  is  no  doubt  that  this  must  be  multiplied  by  a 
large  factor  to  express  the  molecular  composition  :  we  may  write 
it  therefore  (C6HI005)n. 

Boiling  with  dilute  acids  converts  starch  into  glucose. 


C6H10Q5 


H20 


Diastase,  which  is  formed  during  the  germination  of  grain 
(§  307),  converts  starch  into  maltose. 

365.  Dextrin.  —  When  starch  is  heated  to  about  210°,  it  is 
changed  into  a  body  which  is  soluble  in  water,  and  which  is  not 
colored  by  iodine.     It  is  a  pale-yellow  powder,  called  dextrin. 
Its  solution  is  gummy,  and  is  used  as  a  mucilage. 

366.  Gums  are   amorphous  transparent   substances  obtained 
from  certain  plants.     They  form  sticky  liquids  with  water  and 


CELLULOSE.  225 

are  precipitated  by  alcohol.      Gum-arabic   and  gum-tragacanth 
contain  compounds  of  this  description. 

367.  Cellulose  contains  the  same  proportions  of  carbon,  hydro- 
gen, and  oxygen  as  starch.     It  is  the  matter  which  forms  the 
walls  of  young  cells  in  vegetables,  and  is  deposited,  together  with 
other  matters,  in  the  older  cells.     Linen,  cotton,  paper,  and  the 
pith  of  certain  plants  are  almost  pure  cellulose,  which  may  be 
obtained  by  washing  linen  or  cotton  successively  with  dilute  so- 
lution of  potassium  hydroxide,  water,  chlorine-water,  acetic  acid, 
alcohol,  ether,  and  water.     The  insoluble  matter  left  after  these 
operations  is  cellulose. 

It  is  a  translucent,  white  solid,  having  a  density  of  about  1.3. 
It  is  not  soluble  in  any  of  the  ordinary  solvents.  It  dissolves, 
however,  in  the  blue  liquid  obtained  by  shaking  copper  with 
ammonia -water  in  contact  with  the  air.  By  the  action  of  strong 
sulphuric  acid  on  cellulose,  a  gummy  mass  is  obtained,  which 
long  boiling  with  water  converts  into  fermentable  glucose. 

When  paper  is  soaked  in  a  cold  mixture  of  sulphuric  acid  with 
half  its  volume  of  water,  and  is  then  thoroughly  washed  and  dried, 
it  is  converted  into  a  semi-transparent  substance,  which  is  called 
vegetable  parchment.  This  is  the  substance  generally  used  for 
dialysis  (§  220). 

368.  GUN-COTTON  is  made  by  soaking  cotton  wool  in  a  mixture 
of  about  equal  volumes  of  strong  nitric  and  sulphuric  acids,  and 
washing  the  product  in  running  water  until  the  last  traces  of  acid 
are  removed.     After  drying  in  the  air,  the  substance  has  all  the 
appearances  of  cotton,  but  is  not  as  soft  to  the  touch.     It  is  very 
inflammable,  and  burns  with  a  flash,  leaving  no  residue. 

G-un-cottons,  or  nitrocettuloses,  of  which  there  are  several  varie- 
ties, are  the  nitric  ethers  of  cellulose.  The  most  explosive  variety 
is  called  pyroxylin,  and  is  the  hexanitrate,  C12H14(N03)60* ;  it  is 
insoluble  in  water,  alcohol,  and  ether.  Another  variety  is  pro- 
duced when  cotton  is  exposed  for  a  short  time  only  to  the  action 
of  nitric  and  sulphuric  acids.  It  is  quite  soluble  in  a  mixture 
of  alcohol  and  ether,  and  the  solution  is  employed,  under  the 
name  collodion,  in  photography  and  surgery.  This  soluble  form 

15 


226  LESSONS    IN    CHEMISTRY. 

is  a  mixture  of  the  tetranitrate,  C12H16(N03)406,  and  the  penta- 
nitrate,  C12H15(N03)505.  The  gun-cottons  are  now  manufactured 
on  an  enormous  scale  for  use  in  explosives ;  they  are  the  principal 
constituents  of  the  u  smokeless  gunpowders"  and  "blasting 
gelatine."  Celluloid  is  a  mixture  of  nitrocellulose  and  camphor. 
Starch,  dextrin,  the  gums,  and  cellulose  are  polysaccharides. 


LESSON   XLIV. 
BENZENE   DERIVATIVES  (i). 

369.  We  have  already  seen  that  the  unsaturated  hydrocarbon 
benzene,  C6H6,  acts  precisely  like  the  saturated  hydrocarbons,  in 
that  its  compounds  are  formed  by  the  replacement  of  its  hydrogen 
atoms  by  other  atoms  or  groups.     We  have  learned  that  mono- 
chlorobenzene,  C6H5C1,  is  formed  in  this  manner  by  the  replace- 
ment of  an  atom  of  hydrogen  by  one  of  chlorine.     Since  we  may 
consider  that  the  alcohols  are  formed  by  the  replacement  of  one  or 
more  hydrogen  atoms  in  the  saturated  hydrocarbons  by  the  same 
number  of  hydroxyl  groups,  we  can  understand  that  a  similar 
replacement  in  benzene  should  yield  substances  analogous  to  the 
alcohols.  While  these  substances  do  resemble  the  alcohols  in  some 
of  their  chemical  relations,  they  have  at  the  same  time  certain 
other  properties  ;  the  hydrogen  of  their  hydroxyl  is  more  readily 
replaced  by  atoms  of  metal  than  is  that  of  the  alcohols.     They 
are  called  phenols ;  the  most  simple  is  that  in  which  only  one 
hydrogen  atom  is  replaced  by  hydroxyl,  and  it  is  ordinary  phenol, 
commonly  called  carbolic  acid. 

370.  Phenol,  C6H5.OH. — This  important  compound  can  be 
prepared  artificially  from  benzene,  but  it  is  always  obtained  from 
coal-tar,  for  it  is  one  of  the  products  of  the  destructive  distillation 
of  coal.    After  the  benzene  has  been  separated  from  the  tar,  that 
portion  which  distils  during  the  fractional  distillation  between 
150°  and  200°  is  collected  separately,  and  is  mixed  with  a  satu- 
rated solution  of  sodium  hydroxide.     A  compound  in  which  the 


TRINITROPHENOL.  227 

hydrogen  of  the  hydroxyl  in  phenol  is  replaced  by  sodium  is  so 
formed;  this  is  dissolved  in  boiling  water,  and  the  solution  sep- 
arated from  the  oily  matters,  which  remain  unaffected.  The  solu- 
tion of  sodium  phenate  is  then  treated  with  hydrochloric  acid,  the 
reaction  yielding  phenol  and  sodium  chloride. 

C6H5.0Na        +        HCl        =        C6H5.0H        4-        NaCl 
Sodium  phenate.  Phenol. 

The  phenol  is  not  very  soluble  in  water,  and  when  it  has  sep- 
arated is  dried  with  calcium  chloride,  and  distilled.  The  product 
is  then  cooled  in  a  mixture  of  ice  and  salt,  and  the  phenol  forms 
crystals  which  are  separated  and  drained.  » 

Phenol  crystallizes  in  colorless  needles,  melting  at  42°  ;  it  boils 
at  183°.  It  has  a  characteristic  odor,  and  a  burning  taste.  It 
is  only  moderately  soluble  in  water.  Although  it  does  not  red- 
den blue  litmus,  it  readily  reacts  with  the  metallic  hydroxides, 
forming  crystallizable  compounds  which  in  some  respects  resemble 
the  salts.  It  acquires  a  more  or  less  intense  red  color  on  exposure 
to  air  and  light.  Phenol  is  an  exceedingly  valuable  agent  for  the 
destruction  of  low  forms  of  life.  It  prevents  putrefaction  and 
decay  of  animal  and  vegetable  matters,  because  it  prevents  the 
development  of  the  minute  germs  of  life  which  are  the  cause  of 
such  decompositions.  Phenol  is  poisonous,  and  in  a  concentrated 
form  is  quite  corrosive  to  living  animal  tissues. 

When  bromine- water  is  added  to  even  a  very  dilute  solution 
of  phenol,  a  yellow  precipitate  of  tribromophenol,  C6H2Br3(OH), 
is  formed.  A  pine  shaving  dipped  in  phenol  and  then  exposed  to 
the  air  acquires  a  blue  color.  These  properties  aid  us  in  identi- 
fying phenol. 

When  two  hydrogen  atoms  of  benzene  are  replaced  by  hydroxyl  groups,  di- 
atomic phenols,  usually  called  oxyphenols,  result.  They  naturally  have  the 
composition  C6H4(OH)2.  Three  oxyphenols  are  known,  and  we  have  already 
seen  that  we  can  understand  these  cases  of  isomerism  by  attributing  to  the 
hydroxyl  groups  different  positions  in  the  system  of  carbon  atoms  which  are 
so  intimately  related  together. 

371.  Trinitrophenol,  C6H2(N02)3.OH,  commonly  called  picric 
acid,  is  obtained  by  boiling  phenol  with  concentrated  nitric  acid. 
C«H5.0H     +     3HN03    =     C«H2(N02)3.OH     +     SH'O 


228  LESSONS   IN    CHEMISTRY. 

It  crystallizes  from  its  solution  in  boiling  water  in  small,  lemon- 
yellow  scales,  which  are  not  very  soluble  in  cold  water.  It  has 
an  exceedingly  bitter  taste.  It  melts  at  122°.  The  acid  char- 
acter of  trinitrophenol  is  very  pronounced,  and  it  readily  decom- 
poses carbonates.  The  picrates  as  well  as  free  picric  acid  are 
powerful  explosives.  In  solutions  of  picric  acid  animal  fibres, 
such  as  wool  and  silk,  are  dyed  yellow. 

372.  POTASSIUM  PiCRATE,C6H2(N02)3.OK,  may  be  made  by  adding  potassium 
carbonate  to  a  boiling  solution  of  picric  acid  as  long  as  carbon  dioxide  is  dis- 
engaged.    It  forms  long  yellow  needles,  only  slightly  soluble  in  cold  water. 

373.  AMMONIUM  PICRATE,  C6H2(N02)3.ONH*,  is  obtained  by  neutralizing  pic- 
ric acid  with  ammonia-water.    It  burns  with  a  flash,  without  leaving  a  residue, 
and  is  used  in  making  certain  kinds  of  gunpowder  and  colored  fires  ($452). 

374.  Nitrobenzene,  C6H5.N02. — When  benzene  is  added  in 
small  portions  to  a  cold  mixture  of  strong  nitric  and  sulphuric 
acids,  and  the  liquid  is  constantly  stirred,  it  dissolves,  and  when 
this  solution  is  poured  into  cold  water,  a  heavy,  yellowish  oil 
separates.     This  is  nitrobenzene ;  a  hydrogen  atom  of  benzene 
has  been  replaced  by  a  nitro-group,  NO2. 

C6H6     +     HNO3    =     CW.NO2     +     IFO 

Nitrobenzene  boils  at  205°,  and  has  the  specific  gravity  1.2. 
It  has  an  odor  resembling  that  of  bitter  almonds,  and  is  used  in 
perfumery,  especially  for  imparting  an  odor  to  soap.  It  is 
manufactured  in  large  quantities  for  the  production  of  aniline. 

375.  Aniline,  C6H5.NH2. — If  nitrobenzene  be  treated  with  a 
mixture  capable  of  generating  hydrogen,  the  nitro-group  is  re- 
duced, and  converted  into  a  group  NH2.     Almost  all  reducing 
agents  produce  this  change,  but  in  the  arts  iron  and  hydrochloric 
acid  is  used.     The  hydrogen  eliminated  from  the  acid  by  the 
iron,  with  formation  of  ferrous  chloride,  then  reduces  the  nitro- 
benzene to  aniline. 

CW.NO2    +     3H2    =     C6H5.NH*     +     2H20 
Nitrobenzene.  Aniline. 

The  operation  is  conducted  in  large  cast  iron  cylinders  in  which  the  nitro- 
benzene is  continually  stirred  with  the  reducing  mixture.  The  excess  of  acid 
is  then  neutralized  with  lime,  and  the  aniline  formed  distilled  while  steam  is 
passed  through  the  liquid. 

Aniline  is  a  colorless  liquid,  but  becomes  brown  on  long  ex- 


ROSANILINE.  229 

posure  to  the  air.  It  has  an  unpleasant  odor,  and  an  acrid,  burn- 
ing taste.  It  boils  at  184°.  In  water  it  is  but  slightly  soluble, 
but  mixes  in  all  proportions  with  alcohol  and  ether.  Although 
neutral  to  litmus,  it  combines  directly  with  acids,  forming  crys- 
tallizable  salts. 

Aniline  represents  ammonia  in  which  one  atom  of  hydrogen  is  replaced  by 
the  monatomic  group  C6H5.  All  of  the  hydrocarbon  radicals  are  capable  of 
replacing  the  hydrogen  of  ammonia,  and  the  compounds  so  formed  are  called 
compound  ammonias,  or  amines.  Thus,  methylamine,  dimethylamine,  and 
trimethylamine  are  formed  respectively  by  the  replacement  of  one,  two,  and 
three  atoms  of  hydrogen  in  a  molecule  of  ammonia. 

NH3  NH2.CH3  NH(CH3)2  N(CH8)3 

Ammonia.  Methylamine.  Dimethylamine.         Trimethylamine. 

The  group  C6H5,  which  is  benzene  less  one  atom  of  hydrogen,  is  called  phenyl, 
and  phenol  is  then  phenyl  hydroxide,  while  aniline  is  phenylamine. 

376.  To  a  little  aniline  in  a  test-tube,  we  add  a  crystal  of  potas- 
sium nitrate,  and  then  some  strong  sulphuric  acid  ;  a  bright-red 
color  is  produced.     In  another  tube  we  mix  some  aniline  with 
about  twice  its  volume  of  strong  sulphuric  acid,  and  then  drop  in 
a  small  fragment  of  potassium  dichromate ;  a  magnificent  blue 
color  is  developed,  and  becomes  violet  when  the  mixture  is  diluted 
with  water.     A  little  bleaching-powder,  that  is,  chlorinated  lime, 
added  to  aniline  produces  also  a  violet  color.     Similar  reactions 
are  applied  on  a  large  scale  in  the  manufacture  of  numerous 
coloring  matters  derived  from  aniline. 

377.  Ros aniline. — The  benzene  of  commerce  is  not  pure,  it 
contains  much  methylbenzene  or  toluene :  when  it  is  converted 
successively  into  nitrobenzene  and  aniline,  a  nitro-derivative  of 
toluene  is  also  formed,  and  this  is  reduced  to  methylacriline,  just 
as  the  nitrobenzene  is  reduced  to  aniline.     When  such  aniline  is 
heated  with  oxidizing  agents,  both  the  aniline  and  the  methyl- 
aniline  lose  hydrogen  atoms,  and  the  residues  of  the  molecules 
combine,  forming  a  complex  body  called  rosaniline. 

COTN     +     2C'H9N     +     30     =     C20H2iN30     +     2H2Q 
Aniline.        Methylaniline.  Rosaniline. 

Large  quantities  of  rosaniline  are  manufactured  by  heating 
commercial  aniline  either  with  arsenic  acid  or  under  pressure  with 


230  LESSONS   IN   CHEMISTRY. 

nitrobenzene ;  the  oxygen  of  the  arsenic  acid  or  of  the  nitro- 
benzene, removes  hydrogen  from  the  aniline. 

Rosaniline  is  a  colorless  substance,  but  its  salts  have  magnifi- 
cent colors  and  are  used  as  dye-stuffs.  The  rich  red  coloring 
matter  called  magenta  orfuchsine  is  a  compound  of  one  molecule 
of  rosaniline  with  one  of  hydrochloric  acid.  If  a  hot  saturated 
solution  of  this  body  be  treated  with  sodium  hydroxide,  the  color 
disappears ;  sodium  chloride  is  formed,  and  rosaniline  separates 
as  an  almost  colorless,  crystalline  precipitate. 

The  hydrogen  atoms  of  rosaniline  may  be  replaced  by  various 
monatomic  radicals,  such  as  methyl,  ethyl,  phenyl.  The  com- 
pounds formed  by  three  such  replacements  are  more  easily  ob- 
tained than  the  others,  and  the  salts  of  the  resulting  tri-substi- 
tuted  rosanilines  constitute  a  numerous,  varied,  and  valuable 
class  of  coloring  agents,  known  as  the  aniline  dyes. 


LESSON  XLV. 
BENZENE  DERIVATIVES  (2). 

378.  The  hydrocarbons  derived  from  benzene  by  the  replace- 
ment of  its  hydrogen  atoms  by  groups  such  as  methyl  or  ethyl, 
are  capable  of  forming  both  phenols  and  alcohols  ;  for  if  the  re- 
placement of  a  hydrogen  atom  by  hydroxyl  be  in  the  benzene 
radical,  a  phenol  would  result,  while  an  alcohol  would  be  formed 
by  such  a  replacement  in  the  methyl  or  ethyl  group.     Methyl- 
benzene  or  toluene  can  thus  form  an  alcohol,  called  benzyl  alcohol, 
and  three  isomeric  phenols,  which  are  called  cresols. 

C6R5-CH8  HO.C6H*.(CR3)  C6H5.CH2.0H 

Methyl-benzene.  Cresols.  Benzyl  alcohol. 

Our  time  will  permit  the  study  of  only  a  few  of  these  com- 
pounds. 

379.  Benzaldehyde,    C6H5.CHO.  — When    chlorine   gas  is 


SALICYLALDEHYDE. 


231 


passed  through  boiling  toluene,  benzyl  chloride,  C6H5-CH2C1,  is 
formed,  and  by  alkaline  hydroxides  this  may  be  converted  into 
benzyl  alcohol,  C6H5-CH2.OH.  Just  as  ordinary  alcohol  may  by 
slow  oxidation  be  converted  into  aldehyde,  benzyl  alcohol  is  by 
the  action  of  nitric  acid  converted  into  benzaldehyde.  The  latter 
body  is  interesting,  because  it  is  the  essential  part  of  oil  of  bitter 
almonds,  so  much  used  for  flavoring.  The  oil  of  bitter  almonds 
is,  however,  poisonous,  for  it  contains  hydrocyanic  acid,  which,  to- 
gether with  benzaldehyde  and  glucose,  results  from  the  action  of 
water  on  a  substance  called  amygdaKn,  existing  in  the -almonds. 

380.  Benzole  Acid,  C6H5.CO.OH,  exists  naturally  in  gum  ben- 
zoin, and  is  the  product  of  the  oxidation  of  benzaldehyde  and 
benzyl  alcohol.     It  may  be  easily  prepared  from  gum  benzoin,  by 
gently  heating  some  of  that  resin  in  a  shallow  dish,  over  which  is 
pasted  a  piece  of  filter-paper. 

We  cover  the  dish  with  a 
beaker,  and  the  vapor  of  ben- 
zoic  acid  passes  through  the 
paper,  on  which  and  in  the 
beaker  it  condenses  in  beauti- 
ful feathery  tufts  (Fig.  99). 

Benzoic  acid  crystallizes  in 
colorless  needles  or  thin  plates. 
It  melts  at  121°,  and  boils  at 
250°.  It  is  not  very  soluble 
in  cold  water,  but  dissolves  in 
about  twelve  times  its  weight 
of  boiling  water,  and  is  also 
soluble  in  alcohol.  It  is  an 
excellent  antiseptic  or  pre-  pIGi  99. 

servative. 

381.  Salicylaldehyde,  C6H4(OH).CHO.— The  pleasant  odor 
of  essential  oil  of  meadow-sweet  is  due  to  a  compound  repre- 
senting benzaldehyde  in  which  an  atom  of  hydrogen  in  the  ben- 
zene group  is  replaced  by  the  radical  hydroxyl.     It  is  at  the 
same  time  an  aldehyde  and  a  phenol.    It  is  a  colorless  liquid, 


232  LESSONS   IN   CHEMISTRY. 

boiling  at  196°.     It  is  heavier  than  water.     Oxidizing  agents 
convert  it  into 

Salicylic  Acid,  C6H4(OH)CO.OH,  in  which  the  group  CHO 
of  the  aldehyde  has  been  changed  to  carboxyl,  CO. OH.  Salicylic 
acid  is  now  manufactured  by  the  action  of  carbon  dioxide  on 
phenol,  or,  more  correctly,  sodium  phenate.  We  may  represent 
the  reaction 

C6H5.0H         +        CO2        =        C6H*(OH)CO.OH 
Phenol.  Salicylic  acid. 

Salicylic  acid  occurs  as  methyl  salicylate  in  oil  of  wintergreen : 
the  basic  hydrogen,  that  of  the  hydroxyl  group,  is  here  replaced 
by  a  methyl  group,  CH3. 

C6H*(OH).CO.OH  C«H*(OH).CO.OCH3 

Salicylic  acid.  Methyl  salicylate. 

When  oil  of  wintergreen  is  boiled  with  potassium  hydroxide, 
potassium  salicylate  and  methyl  alcohol  are  formed. 

C6H*(OH)CO.OCH3     +     KOH     =     C<5H4(OH)CO.OK     +     CH3.0H 

Salicylic  acid  crystallizes  in  needles  or  prisms  which  are 
scarcely  soluble  in  cold  water,  but  very  soluble  in  boiling  water, 
alcohol,  and  ether.  It  is  largely  used  as  a  preservative,  and  to 
some  extent  in  medicine. 

382.  Gallic  Acid,  C6H2(OH)3.CO.OH.— Salicylic  acid  repre- 
sents benzoic  acid  in  which  one  atom  of  hydrogen  is  replaced  by 
a  hydroxyl  group.  It  is  a  phenol  and  an  acid.  Gall-nuts,  which 
are  little  excrescences  produced  by  the  sting  of  an  insect  on  the 
leaves  and  twigs  of  certain  species  of  oak,  contain  a  substance 
which,  by  continued  exposure  to  air  and  moisture,  undergoes  a 
sort  of  fermentation.  When  the  liquid  is  pressed  from  the  dark- 
colored  mass,  there  remains  a  compound  which  may  be  crystallized 
from  boiling  water  in  long,  colorless,  silky  needles.  It  is  gallic 
acid,  a  compound  which  we  may  consider  as  benzoic  acid  in  which 
three  hydrogen  atoms  are  replaced  by  three  hydroxyl  groups.  It 
is  colorless  and  odorless.  When  carefully  heated,  it  is  converted 
into  a  white  volatile  substance  known  as  pyrogallol,  orpyrogattic 
acid,  while  at  the  same  time  carbon  dioxide  is  disengaged. 

C«H2(OH)3CO.OH  C6H3(OH)3         +         CO2 

Gallic  acid.  Pyrogallol. 


TANNIN.  233 

Gallic  acid  is  quite  readily  soluble  in  water.  Its  solutions, 
especially  if  an  alkaline  hydroxide  be  present,  absorb  oxygen 
from  the  air,  and  become  dark  in  color.  This  last  property  is 
also  common  to  pyrogallol,  a  solution  of  which  is  used  as  a  re- 
ducing agent  in  photography. 

383.  Tannin. — The  well-known  astringent  properties  of  certain 
plants  are  due  to  the  presence  of  compounds  known  as  tannins  or 
tannic  acids,  of  which  there  appear  to  be  a  number  of  varieties. 
They  possess  the  property  of  coagulating  albumen  and  gelatin,  and 
of  forming  black  or  nearly  black  precipitates  with  salts  of  iron. 
Tannin  may  be  extracted  from  gall-nuts  by  placing  the  coarsely- 
powdered  nuts  in  a  funnel  and  pouring  through  them  ether  which 
is  not  free  from  water.  As  the  ether  runs  through,  it  retains  the 
coloring  matters,  while  the  water  in  the  ether  dissolves  the  tan- 
nin, and  the  aqueous  solution  separates  from  the  layer  of  ether 
on  standing.  When  this  solution  is  evaporated  at  a  gentle  heat, 
the  tannin  remains  as  a  light,  very  porous  mass.  It  has  an 
astringent  taste,  and  is  very  soluble  in  water.  When  exposed  to 
moist  air  or  boiled  with  dilute  sulphuric  acid,  it  is  converted  into 
gallic  acid  ;  a  temperature  of  about  210°  decomposes  it,  with  for- 
mation of  pyrogallol  and  carbon  dioxide.  These  reactions  indicate 
that  tannin  is  related  to  gallic  acid,  and  at  least  one  of  its  varieties 
appears  to  be  formed  by  the  union  of  two  molecules  of  gallic  acid 
with  the  loss  of  one  molecule  of  water.  It  is  therefore  digallic  acid. 

2C7H605        =        H2Q        +         C^H^O9 
Gallic  acid.  Digallic  acid. 

The  black  mixture  obtained  by  mixing  solutions  of  tannin  with 
ferric  salts  constitutes  ink.  A  good  black  ink  may  be  made  by 
exhausting  100  grammes  of  powdered  gall-nuts  with  1.4  litres  of 
water,  and  adding  to  the  filtered  liquid  a  solution  of  50  grammes 
of  gum  arabic  and  50  grammes  of  ferrous  sulphate,  each  in  the 
least  quantity  of  water  which  will  dissolve  it.  After  stirring  the 
mixture,  it  is  allowed  to  stand  exposed  to  the  air  until  it  becomes 
quite  black. 

The  operation  of  tanning,  or  the  conversion  of  animal  skins  into 
leather,  depends  on  the  formation  in  the  skin  of  an  insoluble  com- 


234  LESSONS   IN   CHEMISTRY. 

pound  of  tannin  and  the  albuminoid  matter  of  the  skin.  The 
tannin  is  derived  from  oak  bark,  which  is  ground  to  a  coarse  pow- 
der and  piled  in  alternate  layers  with  the  skins  in  deep  vats. 
The  vats  are  then  filled  with  water,  and  the  skins  are  allowed  to 
soak  for  a  few  weeks  or  months,  until  they  have  become  thoroughly 
penetrated  by  the  tannin. 

384.  Camphors.  —  The  highly  aromatic  solids  that  constitute 
the  class  of  bodies  called  camphors  are  derived  from  paramethyl- 
isopropyl-benzene,  or  cymene  ;  it  is  benzene  in  which  two  atoms  of 
hydrogen  have  been  replaced,  one  by  a  methyl  group,  CH3,  the 
other  by  an  isopropyl  group,  C3H7.  Its  composition  is  therefore 
C10HU. 


Benzene.  Cymene. 

Cymene  exists  naturally  in  the  essential  oils  of  chamomile  and 
thyme.  It  is  a  liquid  having  a  pleasant  odor.  Its  relations  to 
the  series  of  camphors  are  indicated  in  the  following  formulae  : 

CIOH",       Cymene. 

C10H140,     Thymol,  or  thyme  camphor. 

C10H160,     Common,  or  Japan  camphor. 

C10H180,     Borneol,  or  Borneo  camphor. 

C10H2°0,     Menthol,  or  mint  camphor. 

385.  THYMOL,  C10HU0,  is  a  phenol,  one  of  the  hydrogen  atoms 
of  the  benzene  group  in  cymene  being  replaced  by  the  group  OH. 
It  exists  in  the  essential  oil  of  thyme,  from  which  it  may  be  ex- 
tracted in  the  form  of  large,  colorless,  crystalline  plates,  fusible 
at  51°.     It  has  a  pleasant  but  penetrating  odor,  and  is  an  ex- 
cellent preservative,  for  it  has  antiseptic  properties,  destroying 
low  forms  of  life. 

386.  COMMON  CAMPHOR,  C10H160,  sometimes  called  laurel 
camphor,  because  it  is  obtained  from  the  camphor  laurel,  a  tree 
which  grows  in  China,  Japan,  and  the  island  Formosa.    It  exists 
in  all  parts  of  the  tree,  but  is  extracted  from  the  wood,  which  is 
chopped  in  small  pieces  and  distilled  with  water.     The  camphor 
vapor  condenses  on  rice-straw,  with  which  the  head  of  the  still  is 
filled  :  it  is  removed  and  purified  by  a  new  sublimation.     It  forms 
semi-transparent,  crystalline  masses  having  a  strong,  aromatic 
odor  and  a  sharp,  burning  taste.    Its  density  at  0°  is  1.    It  melts  at 


INDIGO.  235 

175°,  and  boils  at  209°  ;  it  is  exceedingly  volatile,  and  even  at  or- 
dinary temperatures  it  sublimes  in  the  vessels  in  which  it  is  kept, 
condensing  in  the  upper  part  in  brilliant,  colorless  crystals.  It  is 
almost  insoluble  in  water,  but  dissolves  readily  in  alcohol  and  in 
ether.  When  small  fragments  of  camphor  are  thrown  on  the  sur- 
face of  clean  water,  they  move  around  with  curious  gyratory  move- 
ments, which  are  caused  by  the  pressure  of  the  camphor  vapor 
given  off  in  unequal  quantities  from  different  parts  of  the  surface 
of  the  fragments.  The  currents  of  vapor  may  be  made  evident 
by  dusting  a  small  quantity  of  the  fine  powder  called  lyqopodium 
on  the  surface  of  the  water. 

387.  BORNEOL,  C10H180,  is  obtained  from  an  aromatic  tree  of 
the  Sunda  Isles.     It  forms  small  colorless  crystals,  having  an  odor 
like  that  of  camphor,  but  at  the  same  time  resembling  that  of 
pepper.     It  is  insoluble  in  water,  but  dissolves  in  both  alcohol  and 
ether.     Strong  nitric  acid  converts  it  into  ordinary  camphor. 

388.  MENTHOL,  C10H200,  is  the  solid  part  of  the  essential  oil 
of  mint,  in  which  it  is  mixed  with  a  hydrocarbon  having  the  same 
composition  as   oil  of  turpentine.     It   forms   colorless   crystals, 
fusible  at  36°. 

389.  Indigo,    C16H10N202,    is   prepared   from    several   indigo 
plants,  which  are  cultivated  principally  in  India.     The  leaves  and 
stems  of  these  plants  are  soaked  in  water  for  a  day  or  two ;  a  sort 
of  fermentation  takes  place,  after  which  the  liquid  is  expressed 
and  agitated  in  contact  with  the  air.     A  blue  deposit  forms ;  it  is 
collected  and  boiled  with  water  in  large  copper  vessels,  and  then 
drained,  pressed,  and  broken  up  into  the  fragments  in  which  in- 
digo occurs  in  commerce.     Indigo  results  from  the  decomposition 
of  one  of  its  compounds  which  exists  in  the  plant. 

The  best  indigo  has  a  coppery  appearance.  It  is  not  perfectly 
pure,  but  a  small  quantity  may  be  purified  by  gently  heating  it  in 
a  small  flask  through  which  hydrogen  is  passed :  the  pure  indigo, 
which  is  called  indigotin,  then  sublimes  and  condenses  in  small 
crystals  around  the  cooler  portions  of  the  flask.  It  is  insoluble  in 
water,  alcohol,  and  ether,  but  dissolves  in  strong  sulphuric  acid, 
especially  in  fuming  sulphuric  acid.  The  dark-blue  solution  so 


236  LESSONS    IN    CHEMISTRY. 

obtained  is  commonly  called  sulphate  of  indigo,  and  is  used  in 
dyeing. 

390.  WHITE  INDIGO,  C16H12N202.— When  indigo  is  subjected 
to  the  action  of  reducing  agents,  such  as  sulphurous  acid  and  hy- 
drogen sulphide,  it  is  converted  into  a  dirty-white  substance  called 
white  indigo.  If  a  mixture  of  indigo,  ferrous  sulphate,  and  milk 
of  lime  be  shaken  in  a  corked  bottle,  and  allowed  to  stand  for  a 
day  or  two,  an  alkaline  solution  of  white  indigo  is  obtained,  from 
which  the  latter  may  be  precipitated  by  a  current  of  hydrochloric 
acid  gas.  The  white  indigo  is  insoluble  in  water,  but  dissolves  in 
alcohol  and  in  solutions  of  the  alkaline  hydroxides.  If  a  white 
cloth  be  dipped  in  the  yellowish  solution  in  the  bottle,  and  then 
exposed  to  the  air,  it  rapidly  becomes  blue.  White  indigo,  which 
is  a  compound  of  hydrogen  with  indigo,  is  again  converted  into 
indigo  on  contact  with  the  air,  and  the  experiment  with  the  cloth 
is  an  illustration  of  the  manner  in  which  in  dyeing  the  insoluble 
blue  indigo  is  deposited  in  the  tissues  of  fabrics. 

Indigo  has  been  obtained  artificially  by  a  number  of  interesting 
reactions,  which  will  ere  long  permit  the  manufacture  of  this 
important  dye-stuff  from  the  hydrocarbons  of  coal-tar. 


LESSON    XLVI. 

NATURAL   ALKALOIDS. 

391.  The  compound  ammonias,  derived  from  ammonia  by  re- 
placement of  one  or  more  of  its  hydrogen  atoms  by  various  groups 
or  radicals,  are  powerful  bases.  They  combine  directly  with  acids, 
forming  definite  crystallizable  salts.  Thus,  methyl  ammonium 
chloride  is  as  definite  a  body  as  ammonium  chloride  or  potassium 
chloride. 

KCl  NH4.C1  NH3(CH3).C1 

Potassium  chloride.  Ammonium  chloride.  Methylammonium  chloride. 

An  immense  number  of  compound  ammonias  have  been  formed, 


CONINE.  237 

and  well  studied,  so  that  their  molecular  constitutions  are  perfectly 
known.  Many  plants  contain  principles  most  of  which  have  aot 
been  obtained  artificially,  but  which  so  much  resemble  the  com- 
pound ammonias  in  their  chemical  relations  that  we  believe  them 
to  belong  to  the  same  class.  They  all  contain  nitrogen,  and  it  is 
to  the  nitrogen  atom  or  atoms  that  are  due  the  basic  properties  of 
the  compounds  which  are  called  natural  alkaloids;  that  is,  alkali- 
like  bodies.  Most  of  these  substances  are  poisonous ;  they  all  exert 
peculiar  and  active  effects  on  the  animal  economy. 

392.  The  processes  adopted  for  the  separation  of  the  alkaloids 
from  the  plants  or  vegetable  products  in  which  they  occur,  vary 
according  to  the  solubility  of  the  particular  alkaloid  and  its  salts 
in  various  solvent  agents.     The  alkaloids  do  not  occur  in  an  un- 
combined  state  in  the  plants,  but  united  with  some  natural  acid 
with  which  they  form  salts.    If  the  natural  salt  be  soluble  in  water, 
an  aqueous  extract  of  the  compound  may  be  used  for  the  prepara- 
tion of  the  alkaloid,  but  usually  very  dilute  sulphuric  acid  is  em- 
ployed ;  sometimes  the  plant  or  product  must  be  extracted  with 
alcohol.     The  alkaloid  is  then  set  free  by  the  addition  of  milk 
of  lime  or  other  alkaline  hydroxide,  which  will  form  a  salt  with  the 
natural  acid :  sometimes  the  salt  formed  is  insoluble  in  the  liquid 
employed,  while  the  alkaloid  dissolves ;  sometimes  it  is  the  alka- 
loid which  is  insoluble  and  the  salt  which  remains  in  solution. 
These  circumstances  must  be  investigated,  and  such  a  process 
adopted  as  will  allow  the  alkaloid  to  be  entirely  separated,  and  it 
can  then  be  easily  purified  by  crystallization. 

Two  important  natural  alkaloids  are  liquid;  they  are  conine 
and  nicotine. 

393.  Conine,   C8H15N,  is   the   active   principle   of  poisonous 
hemlock.     It  is  extracted  from  the  seeds,  which  are  crushed  and 
distilled  with  an   alkaline  hydrate.     The   conine  distils,  and  is 
neutralized  with  sulphuric  acid,  which  converts  it  into  a  sulphate, 
of  which  the  solution  is  evaporated  to  a  syrupy  consistence,  and 
then  exhausted  with  a  mixture  of  alcohol  and  ether.     When  the 
alcohol  and  ether  have  been  evaporated,  the  conine  sulphate  is 
distilled  with  a  strong  solution  of  sodium  hydroxide,  and  sodium 


238  LESSONS    IN    CHEMISTRY. 

sulphate  is  formed,  while  the  conine  set  free  condenses,  together 
with  a  little  water.  It  may  be  dried  by  calcium  chloride.  Co- 
nine is  a  colorless,  oily  liquid,  having  a  disgusting  odor.  Only 
slightly  soluble  in  cold  water,  and  still  less  in  hot  water,  it  dis- 
solves freely  in  alcohol  and  ether.  It  is  very  poisonous. 

The  molecular  structure  of  conine  has  been  determined  :  it  is 
one  of  the  few  alkaloids  that  have  been  produced  artificially. 

394.  Nicotine,  C10HUN2,  exists  in  tobacco,  probably  in  combi- 
nation with  malic  acid.     It  may  be  obtained  by  extracting  tobacco 
with  boiling  water,  evaporating  the  filtered  solution  until  it  becomes 
a  pasty  mass,  and  mixing  this  residue  with  about  twice  its  volume 
of  alcohol.     The  alcoholic  liquid  separates  in  two  layers,  of  which 
the  upper  contains  the  nicotine :  it  is  decanted,  and  the  alcohol 
distilled  off.     From  the  residue  the  nicotine  is  set  free  by  potas- 
sium hydroxide,  and  dissolved  out  by  ether.     The  impure  nicotine 
may  then  be  converted  into  an  oxalate  by  the  addition  of  oxalic 
acid,  and  when  this  is  decomposed  by  potassium  hydroxide, 
tolerably  pure  nicotine  is  obtained. 

Nicotine  is  a  colorless  liquid,  having  an  irritating  and  most 
penetrating  odor.  It  is  very  soluble  in  water,  alcohol,  and 
ether.  It  boils  at  241°.  It  is  an  energetic  base,  and  is  one 
of  the  most  active  poisons  known.  Tobacco  contains  from  two 
to  about  seven  per  cent,  of  nicotine,  the  most  esteemed  varieties 
being  those  which  contain  the  least. 

395.  Theobromine,  C7H8N*02,  is  the  alkaloid  of  cacao,  and 
may  be  extracted  from  cacao  beans.     It  is  a  white,  crystalline 
powder,  having  a  bitter  taste,  and  is  not  very  poisonous. 

396.  Caffeine,  C8H10N402,  sometimes  called  theine,  exists  in 
coffee,  tea,  and  several  other  plant  products.     It  may  be  prepared 
by  making  a  strong  tincture  of  tea  with  cold  alcohol,  and  precipi- 
tating the  filtered  liquid  with  basic  lead  acetate.     The  mixture  is 
filtered,  and  freed  from  lead  by  a  stream  of  hydrogen  sulphide, 
after  which  it  is  again  filtered,  evaporated  to  a  small  volume,  and 
while  still  hot  is  treated  with  potassium  hydroxide.     Caffeine  then 
crystallizes  out  as  the  liquid  cools.     It  forms  long,  brilliant,  white 
needles,  containing  one  molecule  of  water  of  crystallization,  which 
is  driven  out  by  a  temperature  of  100°.     It  has  a  bitter  taste ; 


MORPHINE. — ATROPINE.  239 

it  is  not  very  soluble  in  cold  water,  but  dissolves  readily  in  hot 
water  and  in  alcohol. 

Theobromine  and  caffeine  are  related  to  uric  acid,  C6H403N4,  a  body  which 
is  found  in  the  excrements  of  birds  and  serpents,  and  in  urinary  calculi.  By 
the  replacement  of  two  of  its  hydrogen  atoms  by  methyl  we  obtain  theobromine, 
while  caffeine  is  the  trimethyl  derivative. 

397.  Morphine,  C17H19N03.— Opium,  which  is  the  thickened 
juice  of  the  unripe  capsules  of  the  opium  poppy,  contains  several 
alkaloids,  of  which  the  most  important  is  morphine.     The  natu- 
ral salts  in  which  these  alkaloids  exist  in  opium  are  soluble  in 
alcohol ;  laudanum  and  paregoric  are  tinctures  of  opium.     Mor- 
phine may  be  extracted  by  making  a  cold  watery  extract  of 
finely-cut  opium,  evaporating  the  filtered   liquid,  and  adding 
sodium  carbonate  to  the  still  hot  syrup.     In  the  course  of  a 
day  morphine  deposits,  and  may  be  collected  on  a  filter  and 
dissolved  in  dilute  acetic  acid.    -The  filtered  solution  is  then 
decolorized  by  animal  charcoal,  and  the  morphine  again  precipi- 
tated by  ammonia.     Morphine  is  almost  insoluble  in  water,  and 
insoluble  in  ether.     It  is  dissolved  by  hot  alcohol,  from  which  it 
separates  in  crystals  containing  one  molecule  of  water.     It  has  a 
very  bitter  taste. 

When  nitric  acid  is  added  to  a  little  morphine,  an  orange-red 
color  is  produced.  Ferric  chloride  solution  produces  a  blue  color 
with  morphine.  Morphine  forms  easily-crystallizable  salts;  the 
sulphate,,  chloride,  and  acetate  are  used  in  medicine ;  these  salts 
are  soluble,  in  water. 

The  principal  alkaloids  of  opium,  besides  morphine,  are  codeine, 
C18H21N03,  and  narcotine,  C22H23N07 ;  both  are  crystallizable 
solids.  Codeine  is  morphine  in  which  one  hydrogen  atom  is 
replaced  by  methyl. 

398.  Cocaine,  C17H21N04,  exists  in  coca  leaves,  which  are  much 
used  as  a  tonic  and  stimulant  in  South  America.     The  hydro- 
chloride  is  employed  in  medicine  as  a  local  anaesthetic. 

399.  Atropine,  or  Daturine,  C17H23N03,  is  the  alkaloid  ob- 
tained from  the  deadly  nightshade  and  the  thorn-apple.    When 
it  is  administered  internally,  or  applied  to  the  eye,  it  produces 


240  LESSONS    IN    CHEMISTRY. 

dilatation  of  the  pupil,  which  continues  until  all  of  the  alkaloid 
has  passed  from  the  system.     It  is  exceedingly  poisonous. 

400.  Quinine,  C20H2*N202. — Cinchona  bark  contains  several 
alkaloids,  the  more  important  of  which  are  quinine  and  cin- 
chonine. 

These  alkaloids  are  almost  insoluble  in  water,  and  their  sulphates  are  the 
forms  in  which  they  are  principally  employed  in  medicine.  For  the  manu- 
facture of  these  salts,  the  bark  is  extracted  with  very  dilute  sulphuric  acid, 
and  milk  of  lime  added  to  the  clear  solution  to  precipitate  the  alkaloids.  The 
deposit,  containing  also  calcium  sulphate  and  lime,  is  collected,  dried,  and  ex- 
hausted with  boiling  alcohol,  which  dissolves  the  alkaloids.  When  the  filtered 
alcoholic  solution  is  evaporated,  the  cinchonine  crystallizes  first,  being  least 
soluble,  and  the  quinine  is  then  neutralized  with  sulphuric  acid  and  the  solu- 
tion concentrated  until  the  sulphate  crystallizes. 

Quinine  sulphate  crystallizes  in  very  bitter,  delicate  white 
needles,  only  slightly  soluble  in  cold  water,  but  dissolving  in  about 
thirty  times  their  weight  of  boiling  water.  It  dissolves  readily  in 
water  containing  a  little  free  acid.  When  ammonia  is  added  to 
its  solution,  the  free  alkaloid  quinine  is  precipitated  as  a  white 
powder,  while  ammonium  sulphate  is  formed.  Quinine  is  soluble 
in  about  its  own  weight  of  alcohol,  and  in  twenty- two  times  its 
weight  of  ether.  It  is  almost  insoluble  in  water. 

401.  Cinchonine,  C19H22N20,  is  deposited  from  the  alcoholic 
solution  in  which  quinine  still  remains  in  solution  during  its  ex- 
traction from  cinchona  bark.     Its  properties  much  resemble  those 
of  quinine,  from  which,  however,  it  may  be  distinguished  by  its 
insolubility  in  ether.     Quinine  sulphate  supposed  to  contain  cin- 
chonine sulphate  is  treated  with  a  little  ammonia-water,  and  then 
agitated  with  ether;  any  cinchonine   present  will  remain  undis- 
solved. 

402.  Strychnine,  C21H22N202. — The  poisonous  and  medicinal 
properties   of  nux  vomica  are   due   principally  to  two  alkaloids, 
strychnine  and  brucine.     They  are  almost  insoluble  in  water,  and 
may  be  extracted  from  nux  vomica  by  a  process  like  that  which 
serves  for  the  separation  of  quinine.     Tbey  are  both  exceedingly 
bitter,  crystallizable  solids,  nearly  insoluble  in  water.     Strychnine 
is  almost  insoluble  in  alcohol  and  ether,  but  dissolves  in  chloro- 
form.    Brucine  is  soluble  in  alcohol,  and  somewhat  soluble  in  ether. 


METALS.  241 

If  a  small  fragment  of  potassium  dichromate  is  placed  beside 
a  crystal  of  strychnine,  and  both  are  touched  with  a  drop  of  sul- 
phuric acid,  a  rich  blue  color  is  produced,  which  quickly  changes 
to  violet,  purple,  and  red,  and  finally  fades. 

Strychnine  is  a  violent  poison  ;  when  taken  even  in  compara- 
tively trifling  quantities,  it  produces  terrible  convulsions,  resem- 
bling those  of  tetanus. 


LESSON    XLVIL 
METALS.— SPECTRUM  ANALYSIS. 

403.  The  classification  of  the  elements  as  metals  and  non- 
metals  is  more  for  the  sake  of  convenience  than  for  the  indication 
of  absolute  properties  of  either  class.  We  may,  however,  consider 
that  certain  general  properties  are  peculiarly  manifested  by  the 
metals :  they  are  good  conductors  of  heat  and  electricity ;  they 
are  capable  of  acquiring  a  brilliant  lustre,  which  is  called  the 
metallic  lustre.  These  properties  are,  however,  more  or  less  de- 
veloped in  some  of  the  elements  which  we  have  already  studied. 
It  is  not  so,  however,  with  a  chemical  property :  the  metals  are 
capable  of  replacing  the  hydrogen  of  the  oxygen  acids,  forming 
salts.  Some  of  these  salts  we  have  already  studied,  and  we  have 
seen  how  the  combining  power  or  valence  of  a  metallic  atom  is 
indicated  by  the  number  of  hydrogen  atoms  which  it  is  able  to 
replace  in  an  acid.  Yet  even  in  this  respect  the  metals  and  non- 
metals  do  not  seem  to  be  widely  separated,  for  antimony,  which  is 
so  closely  related  to  phosphorus  and  arsenic  by  the  compositions 
and  chemical  natures  of  its  compounds,  is  also  capable  of  forming 
a  few  salts. 

The  physical  properties  of  the  metals  are  most  varied.  They 
are  opaque ;  but  many  of  them  can  be  reduced  to  sheets  so  thin 
that  they  allow  the  passage  of  a  faint  light  whose  color  depends 
on  the  metal  employed.  Their  densities  vary  from  0.59,  that  of 
lithium,  to  22.4,  of  osmium ;  their  freezing  points,  from  39°  below 

16 


242  LESSONS    IN    CHEMISTRY. 

0°,  where  mercury  freezes,  to  about  2500°.  Some,  like  manga- 
nese and  chromium,  are  hard  enough  to  scratch  glass ;  others  are 
soft  enough  to  be  scratched  and  even  cut  by  the  finger-nail,  like 
potassium,  sodium,  and  lead.  Most  of  the  metals  are  malleable  and 
ductile;  they  can  be  beaten  or  rolled  into  sheets  and  drawn  into 
wires.  All  the  metals  are  insoluble  in  water. 

404.  Natural  State  of  the  Metals.— The  condition  in  which 
the  metals  are  encountered  in  nature  depends  upon  the  other 
elements  for  which  they  have  strong  affinities.     Some  of  them 
are  often  found  in  the  metallic  state :  among  these  are  gold,  silver, 
copper,  and  bismuth ;  they  are  then  called  native  metals. 

In  general,  the  elements  which  are  more  usually  combined  with 
the  metals  in  their  ores  are  oxygen,  sulphur,  and  chlorine.  Iron, 
zinc,  and  manganese  are  found  as  oxides ;  iron,  copper,  lead,  mer- 
cury, zinc,  and  silver,  as  sulphides;  sodium  and  silver,  as  chlorides; 
calcium  and  magnesium,  as  carbonates ;  aluminium,  as  silicate. 

The  process  adopted  for  the  extraction  of  a  metal  must  of  course 
depend  upon  the  nature  of  its  ores :  oxides  are  heated  with  char- 
coal ;  carbonates  are  first  heated  to  drive  off  carbon  dioxide,  and  the 
resulting  oxide  is  reduced  by  charcoal.  Sulphides  are  roasted, — 
that  is,  heated  in  the  air, — by  which  the  sulphur  is  converted  into 
sulphur  dioxide,  and  passes  off  in  that  gas,  while  an  oxide  of  the 
metal  is  formed.  The  methods  employed  for  the  reduction  of  the 
chlorides  differ  according  to  the  metal. 

405.  Alloys  are  the  compounds  or  mixtures  which  the  metals 
form  with  one  another.     In  the  molten  state,  many  of  the  metals 
are  capable  of  mixing  with  one  another  in  all  proportions ;  but  by 
certain  precautions,  and  the  use  of  the  proper  proportions  of 
metals,  many  alloys  become  crystallizable,  and  assume  the  proper- 
ties of  true  chemical  compounds :  such  compounds,  of  course,  con- 
tain their  respective  metals  in  the  proportions  required  by  the 
atomic  weights.     The  alloys  of  mercury  are  called  amalgams. 

SPECTRUM   ANALYSIS. 

406.  When  a  beam  of  white  light  is  passed  through  a  prism, 
it  is  dispersed  or  separated  into  a  spectrum  consisting  of  all  the 


SPECTRUM   ANALYSIS.  243 

colors,  from  red  to  violet.  If  the  beam  be  narrow  and  rectangular, 
such  as  is  obtained  by  excluding  all  light  except  that  which 
passes  through  a  rectangular  slit,  and  the  spectrum  be  thrown  on 
a  white  screen,  the  colors  will  not  be  confused,  nor  will  they  be 
distinctly  separate,  but  will  blend  gradually  from  red  to  orange, 
yellow,  green,  blue,  indigo,  and  violet.  When  any  solid  substance 
is  heated  to  bright  incandescence,  it  emits  a  white  light,  whose 
spectrum  will  contain  all  the  prismatic  colors.  We  have  already 
had  occasion  to  observe  the  dazzling  whiteness  of  the  combustion 
of  magnesium  and  phosphorus.  We  have  seen,  also,  that  an  alco- 
holic solution  of  boric  acid  burns  with  a  green  flame.  *We  may 
prepare  alcoholic  solutions  of  sodium  chloride,  strontium  chloride, 
and  barium  chloride,  by  shaking  those  substances  in  separate 
bottles  with  alcohol  which  is  not  too  strong.  When  we  burn 
these  solutions,  we  find  that  the  flame  is  colored  yellow  by  the 
sodium  salt,  red  by  that  of  strontium,  and  green  by  that  of 
barium,  small  quantities  of  the  salts  being  carried  into  the  vapor 
of  alcohol,  and  volatilized  by  the  high  temperature  of  the  flame. 
If  on  the  end  of  a  small  platinum  wire  we  introduce  separately  a 
little  of  each  of  these  salts  into  the  flame  of  an  alcohol  lamp,  or, 
better,  that  of  a  Bunsen  burner,  we  find  that  the  same  coloration 
is  produced.  If  the  light  from  such  a  flame  be  passed  through  a 
narrow  slit,  and  then  through  a  prism,  we  find  that  the  color  is 
invariable  for  each  substance.  The  sodium  salt  produces  not  only 
a  yellow  light,  but  a  particular  shade  of  yellow,  which,  because  it 
has  passed  through  the  straight  slit,  forms  a  peculiar  spectrum, 
consisting  of  a  single  line  of  yellow  light.  If  we  keep  the  slit 
and  prism  in  the  same  positions,  it  matters  not  what  compound 
of  sodium  we  introduce  into  the  flame,  the  same  yellow  line  is 
always  produced,  and  on  the  same  part  of  the  screen.  If  we  in- 
troduce a  little  lithium  chloride  into  the  flame,  the  latter  will  be 
colored  red,  and  we  will  find  on  the  screen  a  red  line  of  a  fixed 
and  constant  shade,  and  always  in  the  same  position. 

Analogous  facts  have  been  discovered  for  all  the  elements,  and 
we  may  say,  generally,  that  while  the  light  emitted  by  an  incan- 
descent solid  depends  upon  the  temperature,  being  first  dull  red, 


244 


LESSONS    IN    CHEMISTRY. 


then  orange,  yellow,  and  white,  an  incandescent  gas  or  vapor,  on 
the  contrary,  always  emits  light  of  a  constant  color,  depending 
on  the  nature  of  the  substance.  Usually  the  spectrum  of  an 
element  does  not  consist  of  a  single  line,  one  color  only,  but  of 
several  and  sometimes  many  lines  ;  but  in  each  case  the  spectrum 
is  peculiar  to  the  element. 

407.  These  principles  have  been  applied  in  spectrum  analysis 
for  the  detection  of  the  elements,  and  the  instrument  employed 
is  called  a  spectroscope.  It  consists  of  a  narrow  slit  at  the  end 
of  a  metallic  tube  containing  a  lens  (A,  Fig.  100),  by  which 


FIG.  100. 

the  rays  of  light  are  made  to  enter  a  prism  in  parallel  lines :  the 
light,  having  passed  through  the  prism,  is  directed  into  a  short 
telescope  (B),  by  which  the  rays  are  again  brought  to  a  focus,  so 
that  the  image  may  be  examined  by  the  eye.  In  order  that  the 
exact  position  of  any  line  may  be  accurately  observed  and  the 
line  identified,  the  image  of  a  small  graduated  scale  illuminated 


SPECTRUM    ANALYSIS.  245 

by  a  faint  light  (C)  is  reflected  into  the  telescope  from  the  side 
of  the  prism  opposite  to  the  slit.  This  scale  corresponds  to  a 
similar  graduated  scale  which  we  might  make  on  a  screen  on 
which  a  spectrum  is  thrown.  The  substance  of  which  the 
spectrum  is  to  be  examined  is  then  heated  on  a  platinum  wire 
in  a  Bunsen-burner  flame  exactly  opposite  the  slit.  Sometimes 
electric  sparks  are  passed  between  points  of  the  substance,  and  if 
the  latter  be  a  gas  it  must  be  enclosed  in  a  tube  and  rendered 
luminous  by  sparks  passed  through  it  from  an  induction  coil.  The 
spectra  of  most  metals  are  very  brilliant  lines  (see  frontispiece), 
so  brilliant  that  they  entirely  obscure  the  more  faint  and  broader 
bands  of  the  spectra  of  the  non-metals ;  for  this  reason,  when  we 
heat  sodium  chloride  in  the  burner  flame,  we  can  only  observe  the 
spectrum  of  sodium  by  the  spectroscope,  although  the  chlorine 
must  also  produce  its  spectrum. 

Spectroscopic  analysis  is  exceedingly  delicate :  s.-oiFff.wu'  °f  a 
milligramme  of  sodium  chloride  introduced  into  the  burner  flame 
will  cause  the  yellow  sodium  line  to  flash  out  for  an  instant. 
While  studying  spectra,  several  chemists  have  observed  lines 
which  were  not  produced  by  any  substance  then  known,  and  have 
thus  been  led  to  the  discovery  of  new  elements,  of  which  small 
quantities  were  present  in  the  substances  under  examination. 

The  study  of  the  spectrum  of  the  sun's  light  and  the  light  of 
the  stars  has  shown  us  perfectly  the  elements  which  exist  in  an 
incandescent  state  in  the  atmospheres  of  those  far- distant  bodies. 
Some  lines  in  the  spectrum  of  sunlight  corresponded  to  those  of 
no  element  known  on  the  earth,  and  chemists  concluded  that  this 
unknown  substance  existed  in  the  sun's  atmosphere,  and  named  it 
helium*  This  same  element  has  recently  been  discovered,  by  the 
aid  of  spectrum  analysis,  in  a  mineral  called  cleveite,  another 
evidence  of  the  distribution  of  the  elements  throughout  the 
universe,  and  of  the  oneness  in  origin  of  all  matter. 

*  Helium  is  a  colorless  gas,  having  a  density  of  2.  Its  molecule  contains  only 
one  atom.  It  seems  to  have  no  affinity  for  other  elements.  Of  all  gases  helium  is 
least  soluble  in  water,  and  most  difficult  to  liquefy.  Its  spectrum  is  character- 
ized by  four  brilliant  lines,  the  colors  of  which  are  red,  yellow,  blue,  and  violet. 


246  LESSONS    IN   CHEMISTRY. 

LESSON    XLVIII. 
METALLIC   COMPOUNDS.— SPECIFIC  HEAT. 

408.  Before  we  undertake  the  study  of  the  individual  metals, 
we  will  pass  in  review  some  of  the  facts  which  we  have  already 
learned  concerning  metallic  compounds,  and  will  develop  them  by 
the  consideration  of  new  details. 

Oxides  and  Hydroxides, — All  excepting  a  few  of  the  metals' 
combine  directly  with  oxygen  at  various  temperatures.  Potassium 
is  the  only  metal  which  is  oxidized  by  cold  dry  air,  and  for  the  ox- 
idation of  some  metals  a  very  high  temperature  is  required.  The 
number  of  atoms  of  oxygen  and  of  metal  which  combine  together 
depends  on  the  atomicity  .of  the  metal.  Two  atoms  of  a  mon- 
atomic  metal  combine  with  one  atom  of  oxygen,  while  in  the  for- 
mation of  a  monoxide  only  one  atom  of  a  diatomic  metal  takes 
part.  The  oxides  of  lithium,  sodium,  and  potassium  are  soluble 
in  water,  but  in  dissolving  they  form  hydroxides,  which  we  must 
admit  contain  a  hydroxyl  group.  These  hydroxides  are  sometimes 
called  hydrates. 

K2Q        +        H2Q        =        2KOH 

The  hydroxides  of  these  three  metals  are  the  alkaline  hydrates, 
the  metals  being  called  the  alkaline  metals.  Nearly  all  the  oxides 
are  capable,  under  certain  conditions,  of  forming  hydrates,  con- 
taining one  or  more  hydroxyl  groups,  and  the  oxidation  or  rusting 
of  metals  in  moist  air  always  results  in  the  formation  of  hydroxides 
and  not  oxides.  Calcium,  strontium,  and  barium  oxides  (or  hy- 
drates) are  less  soluble  in  water  than  those  of  lithium,  sodium, 
and  potassium.  The  other  oxides  are  almost  or  entirely  insoluble 
in  water. 

Some  metals  form  several  compounds  with  oxygen,  and  those 
which  contain  the  least  oxygen  are  basic  oxides,  or  bases ;  they  are 
capable  of  reacting  with  acids,  forming  water  and  salts  in  which 
the  hydrogen  of  the  acid  is  replaced  by  metal.  Most  of  the  oxides 


OXIDES   AND    HYDRATES.  247 

containing  two  atoms  of  oxygen  also  react  with  acids  :  the  forma- 
tion of  the  salt  is  accompanied  either  by  a  disengagement  of 
oxygen  or  chlorine,  or  the  production  of  hydrogen  dioxide. 

BaO2        +     2HC1        =     Bad2         +     H202 

MnO2       +     4HC1        =     MnCl2        +     2H20     +     Cl2 

2Mn02     +     2H2SO*    =     2MnSO*     +     2H20     +     O2 

The  sesquioxides  contain  two  atoms  of  metal  and  three  of 
oxygen.  They  react  with  acids  like  the  lower  oxides,  forming 
the  corresponding  salts  and  water. 

Fe203        +        6HC1  =        2FeCl3  +        3H20 

APO3         +         6HC1  =         2A1CP  +         3H*0 

Fe203        +        3H2SO*        =         Fe2(SO*)3        +        3H20 

In  some  cases,  however,  these  oxides  act  like  acid  radicals. 
Thus  aluminium  sesquioxide  combines  with  sodium  oxide,  pro- 
ducing a  salt-like  body,  aluminate  of  sodium. 

2A1203        +        6NaOH        =        2Al(ONa)3        +        3H20 

Ferric  oxide  combines  with  the  more  basic  ferrous  oxide  to 
form  the  ferroso-ferric  oxide,  FeO.Fe'^O3,  which  constitutes  mag- 
netic iron  ore.  Spinel,  which  may  be  regarded  as  the  type  of 
these  salt-like  bodies,  consists  of  the  oxides  of  aluminium  and 
magnesium,  MgO.APO3. 

The  oxides  containing  one  atom  of  metal  combined  with 
three  or  more  atoms  of  oxygen  correspond  to  metallic  acids. 
They  are  capable  of  reacting  with  water  or  with  basic  oxides, 
forming  well-marked  acids  and  salts.  Chromium  trioxide, 
CrO3,  corresponds  to  chromic  acid,  H2Cr04  =  H20  +  CrO3 ; 
manganese  heptoxide,  Mn'207,  to  permanganic  acid,  HMnO4. 

When  highly  heated  with  charcoal  or  in  a  current  of  hydrogen, 
most  of  the  metallic  oxides  are  reduced  to  metal,  while  either 
carbon  monoxide,  carbon  dioxide,  or  water  is  formed.  The 
oxides  of  calcium,  barium,  strontium,  magnesium,  aluminium, 
potassium,  sodium,  and  lithium  are  not  reduced  by  hydrogen, 
magnesium  oxide  is  not  reduced  by  carbon,  and  some  of  the 
others  only  with  the  aid  of  the  electric  arc. 


248  LESSONS    IN    CHEMISTRY. 

409.  Sulphides. — Nearly  all  the  metals  combine  directly  with 
sulphur  at  certain  temperatures,  and  the  sulphides  formed  are  an- 
alogous in  composition  to  the  oxides.     The  alkaline  sulphides,  and 
those  of  calcium,  strontium,  and  barium,  are  soluble  in  water ;  the 
others  are  insoluble. 

At  temperatures  depending  upon  the  nature  of  the  metal  and 
the  state  of  division  of  the  sulphide,  oxygen  decomposes  all  the 
sulphides,  sometimes  forming  sulphur  dioxide  and  leaving  a  metal- 
lic oxide  or  even  the  free  metal,  sometimes  oxidizing  the  sulphide 
to  sulphate,  according  to  the  nature  of  the  metal.  If  a  mixture 
of  potassium  sulphate  and  powdered  charcoal  be  heated  to  redness 
in  a  covered  crucible,  a  porous  black  mass  is  obtained ;  it  contains 
potassium  sulphide,  and  if  it  be  broken  up  and  thrown  into  the 
air,  this  sulphide  is  oxidized  to  potassium  sulphate,  producing  a 
shower  of  sparks. 

R2S  +       202  K2S04 

Potassium  sulphide.  Potassium  sulphate. 

410.  Chlorides,  Bromides,  and  Iodides. — With  few  excep- 
tions the  metals  combine  directly  with  free  chlorine  ;  since  in  its 
compounds  with  the  metals,  as  in  its  compound  with  hydrogen, 
chlorine  is  a  monatomic  element,  the  number  of  chlorine  atoms 
contained  in  a  molecule  of  a  metallic  chloride  is  an  indication  of 
the  atomicity  of  the  metal. 

All  the  metallic  chlorides  are  soluble  in  water,  excepting  silver 
chloride,  mercurous  chloride,  and  cuprous  chloride :  plumbic 
chloride  is  only  slightly  soluble. 

As  a  rule,  the  bromides  are  more  soluble  than  the  correspond- 
ing chlorides,  and  the  iodides  more  soluble  than  the  bromides. 

411.  The  color  of  the  metallic  compounds  may  be  remem- 
bered by  certain  general  principles.     If  both  the  corresponding 
oxide  or  hydroxide  and  the  corresponding  acid  be  colorless,  the 
salts  are  also  colorless.     If  either  the  acid  or  the  oxide  or  hy- 
droxide be  colored,  the  salts  are  colored.     The  salts  formed  by 
the  same  metal  with  colorless  acids  are  of  about  the  same  color : 
with  colorless  oxides  or  hydroxides  the  same  colored  acid  forms 
corresponding  salts  of  about  the  same  color.     In  many  cases  the 


SPECIFIC    HEAT.  249 

color  of  metallic  compounds  depends  on  water  of  crystallization, 
as  we  have  already  seen  (§  55),  and  is  lost  when  that  water  is 
expelled. 

SPECIFIC    HEAT. 

412.  The  atomic  weights  of  the  metals  cannot  often  be  estimated  from  their 
vapor-densities,  for  many  of  them  are  volatile  only  at  such  high  temperatures 
that  it  is  impracticable,  or  even  impossible,  to  determine  the  densities  of  their 
vapors.  Some  of  the  metals  form  volatile  compounds  with  chlorine  or  with 
various  hydrocarbon  radicals;  and  since  the  molecular  weights  of  these  com- 
pounds can  be  determined  without  difficulty  from  the  densities  of  their  vapors, 
we  can  arrive  at  the  atomic  weight  of  the  corresponding  metal.  • 

The  compounds  of  the  metals  with  oxygen,  with  chlorine,  and  with  other 
bodies  of  course  contain  a  fixed  number  of  atoms  of  metal  with  a  definite 
number  of  atoms  of  other  elements  of  which  the  atomic  weight  is  known. 
Thus,  we  know  that  for  every  sixteen  parts  of  oxygen,  potassium  oxide  con- 
tains 78.2  parts  of  potassium.  We  have  already  studied  the  reasoning  by 
which  we  conclude  that  the  atomic  weight  of  oxygen  is  sixteen ;  how  shall 
we  determine  whether  the  78.2  parts  of  potassium  represent  one,  two,  or  three 
atoms  of  that  metal  ? 

In  order  to  raise  the  temperatures  of  equal  weights  of  different  substances 
through  the  same  number  of  thermometric  degrees,  very  different  quantities 
of  heat  are  required.  If  we  expose  one  kilogramme  of  mercury  and  one  kilo- 
gramme of  water,  both  at  0°,  to  the  same  source  of  heat,  we  find  that  when 
the  water  will  have  been  heated  to  1°  the  mercury  will  be  at  ,30°.  If,  on  the 
other  hand,  we  place  one  kilogramme  of  mercury  at  100°,  with  some  ice,  in  a 
vessel  so  constructed  that  all  of  the  heat  will  be  employed  in  melting  the  ice, 
we  find  that  only  one-thirtieth  as  much  ice  will  be  melted  as  if  we  put  in  the 
same  vessel  one  kilogramme  of  water  at  100°.  The  relative  quantities  of  heat 
which  are  required  to  raise  equal  weights  of  different  substances  through  the 
same  number  of  thermometric  degrees,  are  called  the  specific  heats  of  the  sub- 
stances. Water  is  the  substance  whose  specific  heat  is  chosen  as  unity,  and 
the  specific  heat  of  any  substance  then  represents  the  quantity  of  heat  required 
to  raise  a  given  weight  of  the  substance  through  one  degree,  compared  with 
that  which  will  raise  the  same  weight  of  water  through  the  same  temperature. 
The  specific  heat  of  mercury  is,  then,  -fa  =  0.03333.  On  comparing  the  specific 
heats  of  the  liquid  or  solid  elements,  it  has  been  found  that  just  in  the  same 
proportion  that  the  atomic  weight  increases,  the  specific  heat  diminishes ;  the 
specific  heats  are  inversely  as  the  atomic  weights.  The  product  of  the  specific 
heat  of  any  liquid  or  solid  element  by  its  atomic  weight  should,  then,  always 
give  the  same  figures.  This  important  fact  was  discovered  by  Dulong  and 
Petit,  and  is  generally  called  Dulong  and  Petit's  law:  its  import  is  evi- 
dently that  the  atoms  of  the  different  elements  all  possess  the  same  specific 
heat.  An  examination  of  the  figures  expressing  the  quantities  involved  will 
show  the  facts  on  which  the  law  is  based  : 


250 


LESSONS   IN   CHEMISTRY. 


NAME  OF  ELEMENT. 

ATOMIC  WEIGHT. 

SPECIFIC  HEAT. 

PRODUCT. 

Lithium  

.     ,         7 

0.9408 

6.586 

Boron      

.     ,       11 

0.5 

5.5 

Carbon    

.     .       12 

0.46 

5.52 

.     .       23 

0.2934 

6.748 

Magnesium      .     .     .     .     . 

.     .       24 

0.2499 

5.998 

.     .       27 

0.2143 

5.786 

.     .       31 

0.1887 

5.850 

Sulphur  

.     .       32 

0.2026 

6.483 

Potassium   .     .     „     .     .     . 

.     .       39.1 

0.1695 

6.500 

Zinc  

.     .       65.2 

0.0955 

6.230 

Bromine      

o     .       80 

0.0843 

6.744 

.     .     127 

0.0541 

6.873 

.     o     200 

0.0325 

6.494 

The  average  of  the  products  of  the  atomic  weights  by  the  specific  heats  is 
6.4  :  however,  while  the  product,  which  we  may  call  the  atomic  heat,  is  always 
near  the  number  6.4,  it  varies  within  certain  limits.  Were  it  always  6.4,  we 
could  readily  obtain  the  atomic  weight  of  any  element  by  dividing  6.4  by  the 
specific  heat;  as  it  is,  the  figures  expressing  the  specific  heat  enable  us  to 
choose  between  two  numbers  widely  separated,  and  have  in  several  cases  indi- 
cated that  the  number  which  had  been  supposed  to  represent  the  atomic 
weight  should  be  halved  or  doubled. 


LESSON    XLIX. 
LITHIUM.— SODIUM.— POTASSIUM. 

413.  Lithium,  Li  =  7. — The  metal  lithium  is  very  widely 
diffused  in  nature,  but  is  found  only  in  small  quantity.  As  a 
silicate  or  phosphate  it  forms  an  essential  though  minor  con- 
stituent of  a  number  of  minerals,  such  as  lepidolite  and  triphy- 
lite,  and  other  compounds  of  it  occur  in  spring  waters  and  the 
ashes  of  certain  plants. 

Metallic  lithium  is  obtained  by  decomposing  fused  lithium  chlo- 
ride, LiCl,  a  colorless  soluble  salt,  by  a  current  of  electricity.  It 
is  a  silver-white  metal,  and  does  not  tarnish  in  dry  air.  Its  den- 
sity is  the  lowest  of  any  solid  known,  being  about  0.58.  It  melts 
at  180°,  and  may  be  melted  in  contact  with  the  air  without  be- 
coming oxidized :  when  heated  to  redness  in  the  air  or  in  oxygen, 
it  burns  with  a  dazzling  white  flame.  Lithium  soon  becomes  tar- 
nished in  moist  air,  being  converted  into  lithium  hydroxide, 
LiOH :  when  it  is  thrown  on  the  surface  of  water,  the  same 


SODIUM.  251 

hydrate  is  formed,  the  water  being  decomposed  and  hydrogen 
disengaged.  The  lithium  salts  are  soluble  in  water,  and  are 
colorless  unless  the  corresponding  acid  is  colored.  They  com- 
municate a  red  color  to  the  Bunsen-burner  flame,  and  their  spec- 
trum is  characterized  by  a  brilliant  red  and  a  more  faint  orange 
line  (see  frontispiece). 

414.  Sodium,  Nar=23. — Nearly  forty  per  cent,  of  the  im- 
mense quantities  of  the  common  salt  which  exists  in  the  ocean, 
in  deposits  of  rock-salt,  and  in  -brine  springs,  consists  of  sodium. 
The  metal  may  be  obtained  by  distilling  a  mixture  of  sodium 
carbonate  and  charcoal,  as  described  under  potassium' (p.  254). 

Na'COS     +     20     =     2Na     +     SCO 

A  moie  recent  process  consists  in  reducing  sodium  hydroxide 
by  means  of  a  mixture  of  iron  and  carbon  which  results  when 
finely  divided  iron  and  gas  tar  are  heated  together. 

6NaOH     +     20    =     2Na2C03     +     3H*     +     2Na 
Large  quantities  of  sodium  also  are  now  manufactured  by 
decomposing  the  hydroxide  or  chloride  by  means  of  the  electric 
current. 

Sodium  is  a  white  metal,  so  soft  that  it  can  be  cut  and  moulded 
like  wax.  It  is  lighter  than  water,  its  density  being  0.97.  It 
melts  at  90.6°,  and  boils  at  a  red  heat.  It  can  be  melted  in  the 
air  without  taking  fire.  Its  bright  surface  rapidly  tarnishes  in 
moist  air,  being  converted  into  sodium  hydroxide.  It  is  preserved 
in  bottles  containing  naphtha,  by  which  it  is 
protected  from  the  air.  When  a  small  piece  of 
sodium  is  thrown  on  water,  chemical  action  at 
once  begins  ;  the  sodium  melts  and  rushes  about 
IG'  '  with  a  hissing  noise.  The  reaction  frequently 
terminates  with  an  explosion  by  which  small  particles  of  sodium 
hydroxide  are  thrown  out,  and  we  must  make  the  experiment  at 
a  safe  distance  from  the  eyes.  If  the  motion  of  the  sodium  be 
arrested,  the  heat  will  accumulate  sufficiently  to  ignite  the  escap- 
ing hydrogen.  We  float  a  piece  of  filter-paper  on  some  water  in 
a  plate,  and  throw  on  this  wet  paper  a  small  piece  of  sodium  :  it 
at  once  melts,  and  soon  the  hydrogen  takes  fire,  burning  with  a 
flame  tinged  bright  yellow  by  a  little  sodium  vapor  (Fig.  101). 


252  LESSONS    IN    CHEMISTRY. 

415.  SODIUM  HYDROXIDE,  NaOH,  is  the  product  of  the  reac- 
tion of  sodium  with  water.  It  is  manufactured  by  a  number  of 
processes  :  when  sodium  carbonate  in  rather  dilute  solution  is  boiled 
with  milk  of  lime,  sodium  hydroxide  passes  into  solution,  while 
insoluble  calcium  carbonate  is  formed. 

Na2C03  +  Ca(OH)2  =  2NaOH  +  CaCO3 
This  operation  is  somewhat  expensive,  on  account  of  the  large 
quantity  of  water  which  must  be  boiled  away  from  the  sodium 
hydroxide.  The  Leblanc  process  for  the  manufacture  of  sodium 
carbonate  (§  240)  can  with  slight  modifications  be  made  to  yield 
considerable  quantities  of  an  impure  sodium  hydroxide,  which  re- 
mains in  solution  after  the  sodium  carbonate  has  crystallized. 

Much  sodium  hydroxide  of  an  excellent  quality  is  now  manufactured  from 
cryolite  ($  240).     The  powdered  mineral  is  boiled  with  milk  of  lime,  insoluble 
calcium  fluoride  and  a  solution  of  aluminate  of  sodium  being  obtained. 
AlF3.3NaF     +     3Ca(OH)2    =  =     3CaF2     +     Al(ONa)3     +     3H20 
The  filtered  solution  is  then  boiled  with  a  new  quantity  of  pulverized  cryolite, 
and  all  the  sodium  is  so  converted  into  soluble  sodium  fluoride,  while  alumin- 
ium oxide  is  precipitated. 

Al(ONa)3     +     AlF».3NaF     -     A1203     +     6NaF 

When  the  precipitate  has  settled,  the  clear  solution  is  drawn  off  and  boiled 
with  milk  of  lime :  calcium  fluoride  is  precipitated,  while  sodium  hydroxide 
remains  in  solution. 

2NaF     +     Ca(OH)2     ••     2NaOH     +     CaF2 

By  whatever  process  it  be  obtained,  the  solution  of  sodium 
hydrate  is  evaporated  to  dryness,  and  subsequently  fused  in  iron 
boilers  out  of  contact  with  the  air.  It  then  forms  a  hard,  white 
solid,  which  if  left  exposed  to  the  air  absorbs  moisture  and  car- 
bon dioxide,  becoming  converted  into  sodium  carbonate.  It  is 
very  soluble  in  water,  and  very  caustic.  It  is  commonly  known 
as  caustic  soda,  and  is  employed  in  enormous  quantities  for  the 
manufacture  of  soap. 

Sodium  dioxide,  Na202,  is  made  by  heating  metallic  sodium 
to  about  300°  in  a  mixture  of  nitrogen  and  oxygen  gases  in 
which  the  proportion  of  the  latter  is  gradually  increased.  It  is 
a  yellowish  solid  which  is  decomposed  by  water  into  sodium 
hydroxide  and  oxygen. 

2Na202     +     2H20     =     4NaOH     +     Oa 


SODIUM    CHLORIDE.  253 

Sodium  dioxide  is  a  powerful  oxidizing  agent,  and  is  used  for 
bleaching  animal  fibres. 

416.  SODIUM  CHLORIDE,  NaCl. — This  compound  is  common 
salt.     It  exists  in  numerous  and  immense  deposits  of  rock-salt  in 
many  localities.     It  is  found  in  salt  wells  and  salt   springs,  and 
constitutes  the  greater  portion  of  the  solid  matter  of  sea- water. 
The  water  of  the  Atlantic  Ocean  contains,  according  to  the  local- 
ity, from  32  to  38  grammes  of  solid  matter  per  litre ;  the  water 
of  the  Pacific  contains  somewhat  less,  but  the  average  proportion 
of  common  salt  in  each  is  about  thirty  grammes  per  litre.     The 
other  constituents  of  sea-water  are  principally  chlorides'  and  sul- 
phates of  potassium,  magnesium,  and  calcium,  with  small  quanti- 
ties of  bromides  and  iodides.     When  the  water  is  evaporated,  the 
sodium  chloride  separates  first,  while  the  other  salts  remain  in 
more  concentrated  solution.     In  warm  countries  the  evaporation 
is  often  accomplished  by  the  heat  of  the  sun  and  exposure  to  con- 
stant winds,  in 'large  shallow  basins  into  which  the  water  is  either 
pumped  or  led  by  sluices  from  the  sea. 

Sodium  chloride  crystallizes  in  cubes,  which  may  be  obtained 
of  large  dimensions  and  perfectly  transparent,  by  the  slow  evapo- 
ration of  a  saturated  solution.  It  is  anhydrous,  but  the  crystals, 
especially  if  small,  usually  retain  in  the  spaces  between  them  a 
small  quantity  of  water,  which  is  converted  into  steam  and  causes 
the  crystals  to  decrepitate — that  is,  crack  into  small  pieces — when 
they  are  heated.  It  is  soluble  in  less  than  three  times  its  weight 
of  cold  water,  and  in  about  two  and  a  half  times  its  weight  of 
boiling  water.  It  is  insoluble  in  pure  alcohol.  It  melts  when 
heated  to  redness,  and  volatilizes  at  a  higher  temperature. 

417.  TESTS  FOR  SODIUM. — Since  all  the  ordinary  sodium  salts 
are    soluble  and   colorless,   none   of  the  ordinary  reagents   pro- 
duce either  precipitates  or  colors  in  their  solutions.     Hydrofluo- 
silicic  acid  yields  a  white  precipitate  of  sodium  silico-fluoride 
(§  221).    The  presence  of  sodium  is  easily  detected  by  the  yellow 
color  its  compounds  impart  to  the  Bunsen  flame,  and  by  the 
bright  yellow  line  of  its  spectrum  (see  frontispiece). 

418.  Potassium,    K  =  39. — For  a  long   time   the  principal 


254 


LESSSONS    IN    CHEMISTRY. 


source  of  potassium  compounds  was  the  potassium  carbonate 
obtained  from  wood-ashes.  Large  quantities  of  potassium  car- 
bonate are  now  obtained  from  the  double  chloride  of  potassium 
and  magnesium,  called,  from  its  source,  Stassfurt  salt  (§  242). 
Metallic  potassium  is  prepared  by  decomposing  potassium  car- 
bonate by  carbon  at  a  white  heat.  An  intimate  mixture  of 
potash,  lime,  and  carbon,  obtained  by  heating  crude  argol  *  out 


FIG.  102. 

of  contact  with  the  air,  is  placed  in  an  iron  cylinder,  and  heated 
to  whiteness.  Carbon  monoxide  is  disengaged,  and  the  potas- 
sium vapor  condenses  in  a  flat  receiver,  from  which  the  liquid 
metal  runs  into  vessels  containing  naphtha  (Fig.  102).  Potas- 
sium occurs  in  commerce  as  round,  brownish  masses,  kept 
under  naphtha  for  the  same  reason  that  sodium  is  so  preserved. 
It  is  quite  soft,  and  yields  readily  to  the  pressure  of  the 
finger-nail.  When  freshly  cut,  it  displays  a  brilliant  surface, 
but  this  rapidly  tarnishes  by  the  action  of  the  air.  Its  density 
is  about  0.86 ;  it  melts  at  62.5°,  and  boils  at  a  red  heat,  emit- 
ting a  green  vapor.  When  heated  in  air  it  burns,  forming 
the  oxides  K20  and  K20*.  In  moist  air  it  is  converted  into  the 

*  Argol  contains  considerable  quantities  of  calcium  tartrate. 


POTASSIUM    HYDRATE. 


255 


hydroxide  KOH.  When  a  small  piece  of  potassium  is  thrown 
in  water,  it  decomposes  the  latter  so  violently  that  the  hydrogen 
disengaged  is  at  once  ignited,  and  the  potassium  rushes  about  in 
the  burning  gas,  whose  flame  is  tinged  violet  by 
the  metal  (Fig.  103).  The  experiment  termi- 
nates with  a  little  explosion,  for  the  globule  of 
potassium  hydrate  formed  is  at  a  very  high  tem- 
perature, and  when  it  cools  sufficiently  to  corne 
in  contact  with  the  water,  there  is  a  sudden  for- 
mation of  steam. 

419.  POTASSIUM  HYDROXIDE,  KOH,  is  prepared  by  boiling  milk 
of  lime  with  a  rather  dilute  solution  of  potassium  carbonate.  As 
soon  as  the  reaction  has  terminated,  the  solution  of  potassium  hy- 
droxide is  poured  off  the  deposit  of  insoluble  calcium  carbonate, 
and  is  rapidly  evaporated  to  dryness  in  iron  or  silver  dishes.  It  is 
then  fused,  and  cast  in  cylindrical  moulds  (Fig.  104),  so  that  it 


FIG.  103. 


FIG.  104. 

usually  occurs  in  commerce  in  round  sticks.  It  commonly  contains 
considerable  quantities  of  lime,  potassium  carbonate,  silicate,  and 
other  salts.  It  may  be  purified  by  dissolving  it  in  alcohol  in 
which  only  the  hydroxide  is  soluble,  decanting  the  clear  solution, 
and  fusing  in  a  silver  dish  the  residue  from  which  the  alcohol  has 
been  distilled.  It  is  white  and  opaque,  and  has  a  destiny  of  2.1. 
It  melts  at  a  red  heat,  and  volatilizes  at  a  higher  temperature.  It 


256  LESSONS    IN    CHEMISTRY. 

is  exceedingly  soluble  in  water,  and,  when  exposed  to  the  air,  ab- 
sorbs moisture  and  carbon  dioxide,  deliquescing  to  a  liquid  con- 
sisting of  a  solution  of  the  carbonate.  It  is  very  caustic  and 
corrosive,  rapidly  destroying  animal  tissues.  It  is  employed  in 
making  soft  soap. 

420.  POTASSIUM  CHLORIDE,  KC1. — This  salt  forms  transpar- 
ent, colorless  cubes,  exactly  resembling  the  crystals  of  sodium  chlo- 
ride.    It  is  found  native  in  some  localities,  and,  in  combination 
with  magnesium  chloride,  constitutes  carnattite,  KCl,MgCl2  -f- 
6H20  (see  §  242).     It  dissolves  in  about  three  times  its  weight 
of  cold  water,  and  in  less  than  twice  its  weight  of  boiling  water. 

421.  POTASSIUM  BROMIDE,  KBr,  is  employed  extensively  in 
medicine.      It  is  usually   made  by  adding  to  bromine  enough 
strong  solution  of  potassium  hydroxide  to  almost  decolorize  the 
liquid.     The  reaction  yields  a  mixture  of  potassium  bromide  and 
potassium  bromate. 

6KOH  +  3Br2  =  5KBr  +  KBrO3  +  3H20 
The  mixture  is  evaporated  to  dryness,  and  then  heated  to  red- 
ness, sometimes  with  the  addition  of  a  little  powdered  charcoal ; 
the  bromate  then  loses  its  oxygen,  and  is  converted  into  bromide. 
After  cooling,  the  mass  is  dissolved  in  water,  and  the  salt  made  to 
crystallize.  Potassium  bromide  forms  beautiful  colorless  cubes, 
having  an  intensely  salty  taste,  and  soluble  in  about  one  and  a 
half  times  their  weight  of  cold  water. 

422.  POTASSIUM  IODIDE,  KI,  is  prepared  in  exactly  the  same 
manner  as  the  bromide,  iodine  being  substituted  for  the  bromine. 
It  also  crystallizes  in  colorless  cubes  having  a  salty  and  at  the 
same   time   bitter   taste.      It   dissolves   in   about    two-thirds   its 
weight  of  cold  water,  and  the  solution  will  dissolve  large  quanti- 
ties of  iodine,  becoming  dark  brown  in  color.     Both  the  bromide 
and   iodide  of  potassium  of  commerce  occur  not  in  transparent 
but  in  white,  opaque  crystals :  they  contain  a  trace  of  free  alkali. 
When  the  transparent  crystals  have  been  put  in  the  market,  they 
have  found  no  sale,  being  supposed  to  be  impure. 

423.  TESTS  FOR  POTASSIUM. — Like  the  salts  of  sodium,  most 
of  the  potassium  salts  are  colorless  and  soluble,  and  their  solutions 


SILVER.  257 

are  neither  precipitated  nor  colored  by  the  ordinary  reagents. 
Hydrofluosilicic  acid  produces  a  gelatinous  white  precipitate  of 
silico-potassium  fluoride.  When  the  solution  of  a  potassium  salt 
is  mixed  with  a  strong  solution  of  tartaric  acid,  a  white  crystal- 
line precipitate  of  cream  of  tartar  soon  separates.  Platinic  chloride, 
PtCl*,  produces  a  yellow,  crystalline  precipitate  of  potassium 
chloroplatinate,  (KCl)2PtCl4.  The  potassium  compounds  impart 
a  violet  color  to  flame,  but  the  color  is  rather  delicate,  and  often 
masked  by  the  presence  of  sodium  or  lithium  :  it  is  then  examined 
through  a  blue  glass  which  does  not  allow  the  passage  of  the 
light  from  the  sodium  and  lithium  flames,  but  through  which  the 
violet  potassium  flame  is  distinctly  visible. 

424.  Analogies  of  Lithium,  Sodium,  and  Potassium. — When  we  compare 
together  the  compounds  of  the  metals  which  we  have  just  studied,  we  find 
that  the  three  form  a  group  presenting  the  most  evident  chemical  analogies. 
They  are  monatomic  metals,  capable  of  replacing  the  hydrogen  of  acids,  atom 
for  atom.  One  atom  of  either  metal  will  combine  with  one  atom  of  chlorine, 
or  with  one  hydroxyl  group,  but  two  atoms  are  required  to  combine  with  the 
diatomic  atom  of  oxygen.  Moreover,  the  corresponding  salts  of  these  metals 
are  isomorphous :  they  crystallize  either  in  exactly  the  same  forms,  or  in  forms 
which  are  easily  derived  one  from  the  other.  The  rare  metals  caesium  and 
rubidium  form  part  of  the  group  just  considered. 


LESSON    L. 
SILVER.    Ag  =  108. 

425.  Silver  is  found  in  the  metallic  state,  and  in  combination 
with  many  other  elements,  among  the  more  ordinary  of  which  are 
sulphur,  chlorine,  arsenic,  and  antimony  ;  it  is  frequently  asso- 
ciated with  lead  and  copper. 

When  the  silver  ores  do  not  contain  lead,  the  silver  is  extracted 
by  amalgamating  it  with  mercury  and  then  driving  off  the  latter 
by  the  action  of  heat.  Several  processes  are  employed ;  in  all  of 
them  the  silver  is  first  converted  into  silver  chloride.  The  German 
method  consists  in  roasting  the  powdered  ore  with  common  salt : 
the  sulphides  present  are  thus  oxidized,  while  the  silver  is  con- 
verted into  chloride.  The  cold  mass  is  pulverized,  and  washed 

17 


258  LESSONS    IN    CHEMISTRY. 

with  water  to  remove  all  soluble  salts  formed ;  the  residue  is  then 
put  into  barrels  with  water  and  scrap  iron,  and  these  amalgamation 

barrels  are  rotated  by  machinery 
until  the  contents  are  thoroughly 
mixed  (Fig.  105).  Silver  is  set 
free,  while  the  chlorine  combines 
with  the  iron.  Mercury  is  now 
introduced,  and  forms  an  amalgam 
with  the  silver.  The  liquid  amal- 
gam is  strongly  pressed  in  canvas 
bags,  and  the  greater  part  of  the 
FIG  105  tmntm  mercury  is  squeezed  out.  The 

semi-solid  amalgam  remaining  is 
heated  until  the  mercury  is  expelled,  and  the  residue  is  metallic 
silver  containing  a  certain  proportion  of  copper  derived  from  copper 
sulphide  in  the  ore.  This  method  is  now  obsolete. 

In  the  process  adopted  on  the  Pacific  slope,  the  ore  is  reduced 
to  a  very  fine  powder,  which  is  mixed  with  a  proportion  of  com- 
mon salt  depending  on  the  amount  of  silver  to  be  chloridized. 
By  appropriate  machinery,  this  mixture  is  thrown  into  a  tall 
chimney-shaft  through  which  a  current  of  very  hot  air  is  rising. 
Under  these  circumstances,  all  the  silver  is  at  once  converted  into 
chloride,  which  falls  to  the  bottom  of  the  shaft,  from  which  it  is 
removed  when  about  a  ton  has  accumulated.  It  is  then  washed 
in  a  stream  of  water,  and  the  insoluble  silver  chloride  settles  as 
a  pulpy  mass.  This  pulp  is  mixed  with  a  little  cupric  sulphate 
and  common  salt  in  iron  pans  heated  by  steam,  and  about  one 
hundred  and  fifty  pounds  of  mercury  are  added  for  every  ton  of 
the  pulp.  After  five  or  six  hours'  grinding,  the  mercury  contains 
all  the  silver,  which  is  reduced  partly  by  the  iron  of  the  pan, 
partly  by  the  conversion  of  some  mercury  into  chloride.  The 
amalgam  is  then  agitated  with  water,  and,  after  it  is  dried,  the 
mercury  is  driven  off  by  distillation  in  cast-iron  retorts. 

426.  Galena,  or  lead  sulphide,  an  important  lead  ore,  often  con- 
tains a  considerable  proportion  of  silver,  which  forms  an  alloy  with 
the  lead  when  the  ore  is  reduced.  Large  quantities  of  silver  are 


SILVER.  259 

extracted  from  such  lead  by  a  process  called,  from  the  name  of  its 
inventor,  Pattinsonizing.  When  a  melted  alloy  of  lead  and  sil- 
ver containing  even  small  quantities  of  the  latter  metal  is  allowed 
to  cool,  almost  pure  lead  first  solidifies  in  crystals  ;  this  is  the  fact 
on  which  the  process  is  based.  The  molten  lead  is  allowed  to 
cool  slowly,  and,  by  means  of  large  ladles,  the  crystals  of  lead  are 
removed  as  fast  as  they  are  formed,  so  that  the  metal  which 
remains  liquid  to  the  last  is  an  alloy  rich  in  silver  (Fig.  106). 


FIG 


As  the  lead  crystals  so  removed  still  contain  a  little  silver,  they 
are  submitted  a  second  and  a  third  time  to  the  same  operation,  so 
that  pure  lead  is  obtained  on  one  hand,  and  a  very  rich  silver  alloy 
on  the  other.  The  lead 'is  entirely  removed  from  the  alloy  by 
a  process  called  cupellation.  The  metal  is  melted  on  a  shallow 
hearth  swept  by  the  flame  of  a  small  furnace.  This  hearth,  which 


260 


LESSONS    IN    CHEMISTRY. 


is  called  a  cupel,  is  covered  by  a  sheet-iron  dome  (Gr,  Fig.  107), 
which  can  be  raised  and  lowered  as  necessary.     When  the  whole 


FIG.  107. 

of  the  metal  is  melted,  a  blast  of  air  is  blown  on  its  surface  from 
pipes  called  tuyeres  (t  *),  and  the  lead  is  oxidized.  The  oxide 
melts,  and,  being  lighter  than  the  metal,  is  drawn  off  through  a 
notch  cut  in  the  side  of  the  cupel,  and  the  notch  is  gradually 
deepened  as  the  level  of  the  fused  metal  becomes  lowered.  The 
silver  does  not  oxidize,  and  at  last,  when  its  surface  is  covered  with 
only  a  thin  layer  of  molten  lead  oxide,  that  layer  breaks  suddenly, 
and  the  brilliant  surface  of  the  silver  appears  with  a  flash.  The 
blast  of  air  is  then  stopped,  and  the  silver  is  either  drawn  off  into 
ingot-moulds  or  allowed  to  solidify  in  the  cupel. 

427.  Silver  is  the  most  brilliantly  white  metal.  It  is  exceed- 
ingly malleable  and  ductile.  Its  density  is  10.5.  It  does  not 
tarnish  on  exposure  to  the  air,  but  above  its  melting  point,  which 
is  about  1000°,  it  absorbs  or  combines  with  about  twenty-two  times 
its  volume  of  oxygen  from  the  air.  The  oxygen  is  expelled  vio- 
lently as  the  metal  solidifies,  and  portions  of  the  still  liquid  silver 
are  often  projected  from  the  vessel,  while  its  surface  is  thrown  into 
curious  tree-like  forms.  This  phenomenon  is  called  "  spitting." 


SILVER   CHLORIDE   AND   OXIDE.  261 

Ozone  oxidizes  silver  to  the  dioxide  Ag202.  It  is  blackened  by 
Hydrogen  sulphide,  silver  sulphide  being  formed  on  its  surface ; 
the  discoloration  of  silver-ware  is  due  to  traces  of  hydrogen  sul- 
phide in  the  air ;  the  sulphur  in  eggs,  mustard,  etc.,  rapidly 
blackens  silver  spoons.  Boiling  sulphuric  acid  dissolves  silver 
slowly,  converting  it  into  sulphate ;  hydrochloric  acid  forms  in- 
soluble silver  chloride  on  its  surface,  and  the  metal  beneath  is  so 
protected  from  further  action.  It  dissolves  readily  in  nitric  acid, 
red  vapors  being  disengaged  and  silver  nitrate  formed.  It  is  not 
attacked  by  the  alkaline  hydroxides,  and  therefore  silver  vessels 
are  used  for  the  concentration  and  fusion  of  those  compounds. 

428.  SILVER  CHLORIDE,  AgCl,  is  one  of  the  more  important 
silver  ores ;  it  is  the  mineral  horn-silver,  so  called  from  its  ap- 
pearance and  somewhat  elastic,  horn-like  structure.      We  have 
already  seen  that  it  is  precipitated  on  the  addition  of  hydrochloric 
acid  or  a  soluble  chloride  to  solution  of  silver  nitrate.     It  then 
forms  a  white,  curdy  precipitate,  which  darkens  and  undergoes 
partial  decomposition  on  exposure  to  light.     If  a  piece  of  zinc  be 
placed  in  some  recently- precipitated  and  still  moist  silver  chloride, 
the  whole  of  the  silver  soon  separates  in  the  form   of  a  gray 
powder,  while  zinc  chloride  is  formed.     Pure  silver  may  be  thus 
obtained,  but  for  that  purpose  the  silver  chloride  should  be  pre- 
viously well  washed  with  dilute  sulphuric  acid,   and  the  silver 
powder  must  be  thoroughly  washed  by  shaking  it  many  times 
with  water  and  then  allowing  it  to  settle.     Pure  silver  may  also 
be  made  by  fusing  the  well-washed  chloride  with  sodium  carbon- 
ate ;  carbon  dioxide  and  oxygen  are  disengaged,  sodium  chloride 
is  formed,  and  the  silver  remains  as  a  button  at  the  bottom  of  the 
crucible.     When  recently  precipitated,  silver  chloride  dissolves 
readily  in  ammonia-water,  from  which  it  is  again  deposited  when 
the  ammonia  is  neutralized  by  an  acid. 

429.  SILVER  OXIDE,  Ag20,  is  made  either  by  precipitating  a 
solution  of  silver  nitrate  by  potassium  hydroxide,  or  by  boiling 
well-washed  silver  chloride  with  potassium  or  sodium  hydroxide  so- 
lution.    It  is  a  brown  powder,  insoluble  in  water,  and  decomposed 
by  heat  into  silver  and  oxygen. 


262  LESSONS    IN    CHEMISTRY. 

430.  SILVER  SULPHIDE,  Ag2S,  is  found  native  in  small  octa- 
hedral crystals.     It  is  precipitated  by  the  action  of  hydrogen  sul- 
phide on  solution  of  silver  nitrate,  and  may  be  formed  by  the  direct 
union  of  silver  and  sulphur  at  a  slightly-elevated  temperature. 

431.  TESTS  FOR  SILVER. — In  solutions  of  silver  salts,  hydro- 
chloric acid  produces  a  white  precipitate  of  silver  chloride ;  this 
precipitate  is  soluble  in  ammonia-water,  and  darkens  in  color  when 
exposed  to  light.     Potassium  iodide  solution  gives  a  yellow  pre- 
cipitate of  silver  iodide,  Agl,  which  also  darkens  by  the  action  of 
light,  but  is  only  slightly  soluble  in  ammonia.    Hydrogen  sulphide 
precipitates  black  silver  sulphide.    Potassium  chromate  precipitates 
red  silver  chromate,  Ag2Cr04,  in  neutral  solutions  which  are  not 
too  dilute. 

432.  SILVER-PLATING. — It  is  often  desired  to  cover  other  metals  or  glass 
with  a  thin  layer  of  silver.     This  may  he  accomplished  in  several  manners. 
Copper  objects   may  be  silvered  by  rubbing  them  with  a  mixture  of  moist 
silver  chloride  and  sodium  carbonate,  but  the  layer  of  silver  so  deposited  is 
very  thin.     The  metals  are  most  readily  and  evenly  silvered  by  connecting 
the  object  to  be  plated  with  the  zinc  pole  of  a  voltaic  battery  and  immersing 
it  in  a  solution  of  silver  and  potassium  double  cyanide,  made  by  boiling  silver 
chloride  in  a  solution  of  potassium  cyanide.     The  positive  pole  of  the  battery 
is  connected  with  a  plate  of  silver,  or  silver  coin,  immersed  in  the  same  liquid. 
The  silver  solution  then  always  retains  its  strength,  for  the  metal  dissolving 
from  the  positive  electrode  replaces  that  which  is  deposited  on  the  article  to 
be  silvered.     We  may  readily  coat  the  interior  of  a  test-tube  with  a  thin  layer 
of  silver  by  pouring  into  it  a  solution  of  silver  nitrate  and  sufficient  ammonia- 
water  to  redissolve  the  precipitate  first  formed  :  we  then  add  a  few  drops  of  a 
solution  of  tartaric  acid,  and  place  the  tube  in  water  heated  to  about  50°.     A 
flat  piece  of  glass  may  be  silvered  by  the  same  liquid,  which  is  then  poured 
on  in  just  sufficient  quantity  to  cover  evenly  the  perfectly-cleaned  glass.    The 
layer  of  silver  so  formed  is  very  thin,  and  allows  the  passage  of  a  violet  light. 

433.  ASSAYING  OP  SILVER. — The  term  assaying  means  determining  the  pro- 

portion of  pure  metal  in  either  an  alloy  or  an  ore,  but 
is  now  usually  restricted  to  the  first.  Silver  is  alloyed 
with  copper,  and  the  alloy  may  be  assayed  either  by  a 
dry  process — that  is,  one  in  which  no  liquid  is  employed 
— or  by  a  wet  process.  The  dry  process  consists  in  melt- 
FlG.  108.  ing  a  small  quantity  of  lead  in  a  cupel,  which  is  a  little 

shallow  cup  made  of  compressed  bone-ash  and  is  very 

porous  (Fig.  108).    A  weighed  quantity  of  the  silver  coin  or  jewelry  to  be  as- 
sayed is  then  wrapped  in  a  small  piece  of  paper  and  placed  on  the  surface  of 


SILVER    ASSAY. 


263 


the  melted  lead,  in  which  it  is  quickly  dissolved.  The  cupel  is  heated  in  a 
muffle  (A,  Fig.  109)  which  fits  into  an  opening  in  the  side  of  a  muffle-furnace. 
The  muffle  is  open  only  at  the  exterior  end,  and  has  a  slit  in  the  arched  top, 
so  that  the  air  is  drawn  through  it  by  the  draught  of  the  furnace.  The  lead  is 
oxidized  by  the  air,  and  in  presence  of  lead  the  copper  of  the  alloy  becomes 
also  converted  into  oxide ;  the  fused  oxides  are  absorbed  by  the  porous  cupel, 
and  as  soon  as  their  last  traces  disappear,  the  flashing  of  the  bright  silver 
surface  indicates  that  the  operation  is  finished.  When  cold,  the  button  of 
pure  silver  is  weighed. 

The  wet  assay  is  an  example  of  volumetric  analysis  which  we  must  study. 
We  know  that  by  the  addition  of  a  solution  of  common  salt  to  one  of  silver 
nitrate,  silver  chloride  is  precipitated,  and,  since  one  molecule  of  sodium  chlo- 
ride reacts  with  one  molecule  of  silver  nitrate,  we  find  that  58.5  parts  .by  weight 
of  salt  will  precipitate  exactly  108  parts  of  silver  in  the  form  of  chloride. 

NaCl         +         AgNO3         =         AgCl         +         NaNO3 

(23  +  35.5)  (108  +  14  +  48)  (108  +  35.5)  (23  +  14  +  48) 

By  carefully  adding  a  solution  of  common  salt  to  a  solution  of  silver  nitrate, 
we  can  tell  when  all  the  silver  has  been  converted  into  chloride,  for  no  more 
precipitate  is  then  formed.  Now,  if  we  know 
how  much  salt  we  have  added,  we  can  easily 
calculate  how  much  silver  was  pres- 
ent, because  every  58.5  parts  of  salt 
used  will  represent  1 08  parts  of  silver 
precipitated.  Let  us  make  a  solu- 
tion of  salt  of  which  each  litre  shall 
precipitate  ten  grammes  of  silver. 
Since  108  grammes  of  silver  require 
58.5  grammes  of  salt,  10  grammes  of 

silver  will   require   58'5  X  10  =  5.417 

108 

grammes  of  salt.  We  make  such  a 
solution,  and  we  know  that  every 
cubic  centimetre  of  it  will  precip- 
itate 10  g™mmes  -1  centigramme  of 
1000 

silver.  We  now  dissolve  in  nitric 
acid  about  a  gramme  of  our  alloy  of 
silver,  accurately  weighed,  and  then 
introduce  our  salt  solution  into  a 
burette  (Fig.  110),  which  is  a  glass  FlG.  110. 
tube  having  a  stop-cock  at  the  bot- 
tom, and  graduated  so  that  we  may  measure  how  much  of  the  liquid  we  allow 
to  run  out.  Then  the  salt  solution  is  slowly  dropped  into  the  solution  of  silver 
nitrate,  which  is  agitated  so  that  the  precipitate  may  quickly  settle,  until  the 
instant  arrives  when  a  drop  produces  no  precipitate.  We  then  carefully  read 


FlG.  109. 


264  LESSONS    IN    CHEMISTRY. 

off  the  exact  quantity  of  salt  solution  used,  and  calculate  the  amount  of  silver 
present  in  the  quantity  of  alloy  analyzed,  eacli  cubic  centimetre  of  the  salt 
solution  representing  0.01  gramme  of  silver. 

The  silver  coins  of  the  United  States  contain  90  per  cent,  of  silver  and  10 
per  cent,  of  copper. 

434.  PHOTOGRAPHY. — The  chloride,  bromide,  and  iodide  of 
silver,  being  partially  decomposed  by  the  action  of  light,  are  em- 
ployed in  photography.  An  image  of  the  object  to  be  photo- 
graphed being  thrown  on  a  glass  plate  coated  with  either  of  these 
sensitive  salts,  those  portions  on  which  the  light  falls  are  dark- 
ened, and  metallic  silver  is  formed ;  the  shades  or  dark  parts  of 
the  image  remain  unaffected  in  proportion  to  the  intensity  of  the 
shade :  then  when  the  plate  is  placed  in  a  liquid  capable  of  dis- 
solving the  unaltered  salts,  a  negative  photograph  is  obtained ;  that 
is,  one  in  which  the  natural  lights  and  shades  are  reversed.  This 
negative  being  placed  over  a  paper  sensitized  by  some  compound 
alterable  by  light,  a  positive  picture  is  obtained,  for  the  light  acts 
through  the  transparent  portions  of  the  negative.  We  can  easily 
make  a  sensitive  paper  by  soaking  a  piece  of  soft  white  paper  in 
a  solution  of  common  salt,  and,  after  drying  it,  putting  it  in  a 
solution  of  silver  nitrate  in  a  dark  room.  Silver  chloride  is  thus 
formed  in  the  paper.  If  now  we  have  a  negative  or  drawing  on 
glass,  we  may  make  a  photograph  ;  or  we  may  copy  some  leaves 
by  placing  them  on  the  paper,  and,  after  pressing  them  down  un- 
der a  glass  plate,  expose  the  whole  to  the  action  of  sunlight.  In 
a  quarter  of  an  hour  we  remove  the  plate,  and  soak  the  paper  in 
a  solution  of  sodium  thiosulphate  (§  106),  which  dissolves  out  the 
unaltered  silver  chloride :  this  is  necessary,  since  the  light  would 
otherwise  blacken  the  paper  uniformly.  After  thoroughly  wash- 
ing the  paper  in  water,  we  have  an  exact  copy  of  the  negative  or 
leaves  employed. 


CALCIUM.  265 

LESSON    LT. 

CALCIUM.— STRONTIUM.— BARIUM. 

435.  These  three  elements  form  a  group  of  metals  of  which  the  correspond- 
ing compounds  not  only  present  remarkable  chemical  analogies,  but  resemble 
one  another  in  many  physical  properties.  We  have  already  had  occasion  to 
notice,  during  the  study  of  certain  of  their  salts,  that  they  are  diatomic  ele- 
ments, capable  of  replacing  two  atoms  of  hydrogen  in  the  acids. 

The  metals  are  obtained  by  decomposing  their  fused  chlorides  b'y  a  power- 
ful electric  current.  They  are  harder  than  lead,  and  their  surfaces,  which  are 
brilliant  when  freshly  filed,  rapidly  tarnish  in  moist  air.  They  decompose 
cold  water,  forming  hydrates  while  hydrogen  is  disengaged ;  when  heated  in 
the  air  or  in  oxygen,  they  take  fire  and  burn  brilliantly. 

436.  Calcium,  Ca  =  40,  is  the  metallic  radical  of  lime,  marble, 
gypsum,  etc.     Its  density  is  about  1.6. 

437.  CALCIUM  CHLORIDE,  CaCl2,  may  be  made  by  dissolving 
white  marble  in  hydrochloric  acid.     It  is  now  obtained  in  large 
quantities  as  an  accessory  product  in  the  manufacture  of  sodium 
carbonate  by  the  ammonia  process.     It  crystallizes  in  large  color- 
less prisms  containing  six  molecules  of  water  of  crystallization. 
These  crystals  are  deliquescent ;  when  they  dissolve  in  water,  in 
which  they  are  very  soluble,  they  produce  a  marked  lowering  of 
temperature.     A  mixture  of  equal  weights  of  crystallized  calcium 
chloride  and  snow  or  broken  ice  produces  a  temperature  of — 45°. 
When  heated,  the  crystals  melt,  and  at  200°  four  molecules  of 
water  are  driven  out,  but  the  other  two  are  retained  until  the 
temperature  reaches  redness.     As  the  anhydrous  calcium  chloride 
cools,  it  then  solidifies  to  a  hard,  white,  crystalline  mass ;  this  is 
used  for  drying  gases  and  liquids  with  which   it  undergoes   no 
chemical  reaction.     Its  solution  in  water  develops  considerable 
heat. 

A  saturated  solution  of  calcium  chloride  boils  at  179.5°.  The 
low  cost  of  calcium  chloride  obtained  in  the  ammonia-soda  pro- 
cess has  permitted  the  adoption  of  a  new  and  very  cheap  process 
for  the  extraction  of  sulphur  from  the  earthy  matters  with  which 


266 


LESSONS     IN     CHEMISTRY. 


it  occurs.  The  sulphur  ore  is  immersed  in  a  hot  solution  of  cal- 
cium chloride  of  such  strength  that  it  boils  at  about  120°  ;  the 
sulphur  then  melts  and  runs  out  of  the  earthy  matters,  and  may 
be  drawn  off  as  it  collects  below  the  hot  liquid. 

438.  CALCIUM  OXIDE,  CaO. — This  substance  is  universally 
known,  and  commonly  called  lime.  It  is  manufactured  by  de- 
composing limestone,  which  is  calcium  carbonate,  by  the  action 
of  heat,  but  it  is  necessary  that  the  products  of  combustion  shall 
pass  through  the  heated  mineral,  for  calcium  carbonate  is  decom- 
posed only  at  exceedingly  high  temperatures  when  heated  in  cov- 
ered vessels.  Very  primitive  furnaces  or  lime-kilns  are  usually 
employed,  resembling  holes  in  the  side  of  a  hill :  above  an  open- 
ing at  the  bottom  a  sort  of  grate  is  arranged,  and  on  this  the  coal 
and  limestone  are  thrown  from  the  top.  The  tire  is  then  lighted, 
and  in  about  three  days  the  kiln  is  burned  out.  A  continuous 


FIG.  111. 

and  more  economical  lime-kiln  has  an  opening  at  the  base  for  the 
removal  of  the  lime,  and  about  three  metres  above  this  opening 
there  are  others  by  which  the  flames  from  furnaces  pass  directly 
into  the  mass  of  limestone.  As  the  lime  is  raked  out  at  the  bot- 
tom, the  limestone  descends,  and  more  is  thrown  in  at  the  top 
(Fig.  111). 


LIME.  267 

Lime  occurs  in  hard,  compact  masses  of  a  white  or  gray  color  : 
it  is  called  quick-lime.  It  is  infusible  at  the  highest  temperatures 
which  we  can  produce  by  combustion,  but  may  be  melted,  and 
even  volatilized,  in  the  electric  furnace :  the  molten  mass  crys- 
tallizes upon  cooling.  When  exposed  to  the  air,  it  absorbs 
moisture  and  carbon  dioxide,  cracks,  increases  in  volume,  and 
crumbles  to  a  white  powder,  which  consists  of  a  mixture  of  cal- 
cium hydroxide  and  calcium  carbonate.  When  a  mass  of  lime  is 
sprinkled  with  water,  the  latter  is  absorbed ;  in  a  short  time  the 
lime  becomes  so  hot  that  steam  is  given  off,  and,  insufficient 
water  be  used,  the  whole  falls  to  a  bulky  powder  of  calcium  hy- 
droxide, Ca(OH)2,  which  is  called  slaked  lime.  Lime  which  de- 
velops much  heat  and  increases  greatly  in  volume  by  hydration 
is  called  fat  lime,  but  if  there  be  little  heat  produced,  and  the 
volume  not  greatly  augmented,  the  lime  is  said  to  be  poor  lime  ; 
it  then  contains  considerable  quantities  of  impurities. 

Milk  of  lime  is  calcium  hydroxide,  that  is,  slaked  lime,  sus- 
pended in  water.  If  this  white,  creamy  liquid  be  allowed  to 
settle,  the  clear  liquid  obtained  is  lime-water.  This  is  a  solution 
of  calcium  hydroxide,  which  dissolves  in  about  seven  hundred 
times  its  weight  of  cold  water.  It  is  only  about  half  as  soluble 
in  boiling  water.  When  lime-water  is  heated,  it  becomes  turbid 
from  the  separation  of  part  of  the  hydroxide,  which  again  dis- 
solves as  the  liquid  cools. 

Large  quantities  of  lime  are  employed  in  building  operations. 
Ordinary  mortar  is  a  mixture  of  slaked  lime  and  sand,  the  prin- 
cipal object  of  the  latter  being  to  prevent  the  shrinking  of  the 
mortar  as  it  dries.  Mortar  hardens  because  the  calcium  hydroxide 
gradually  absorbs  carbon  dioxide  from  the  air,  and  the  calcium 
carbonate  formed,  adhering  strongly  to  the  surfaces  with  which  it 
is  in  contact,  binds  them  together.  It  is  possible  that  a  small 
proportion  of  calcium  silicate  is  also  formed  during  the  hard- 
ening. 

Cements,  of  which  Portland  cement  *  is  an  excellent  type,  are 


*  Named  from  its  resemblance  to  Portland  stone. 


268 


LESSONS   IN    CHEMISTRY. 


made  by  calcining  limestone  with  from  ten  to  thirty  per  cent,  of 
clay.  Sometimes  the  clay  exists  naturally  in  the  limestone ;  some- 
times it  is  added  in  the  form  of  dried  river-mud.  Clay  is  a  hy- 
drated  aluminium  silicate,  and  is  rendered  anhydrous  by  the  action 
of  heat.  It  is  probable  that  at  the  same  time  a  little  calcium  sili- 
cate and  aluminate  of  calcium  are  formed.  However  that  may  be, 
the  hard  mass  resulting  from  the  calcination  is  pulverized,  and 
the  powder  is  cement,  or  hydraulic  lime.  When  it  is  mixed  with 
water,  it  sets,  or  hardens  to  a  solid  mass,  in  a  very  short  time.  It 
has  the  property  of  hardening  under  water,  and  is  invaluable  in 
submarine  architecture.  Its  hardening  is  apparently  due  to  the 
formation  of  a  double  silicate  of  aluminium  and  calcium. 

439.  CHLORINATED  LIME,  CaCl(ClO). — This  compound,  which 


FIG.  112. 

is  intermediate  between  calcium  chloride,  CaCl2,  and  calcium  hy- 
pochlorite,  Ca(ClO)2,  is  manufactured  on  an  extensive  scale  by 
passing  chlorine  gas  over  well-slaked  lime  placed  in  thin  layers 
on  shelves  in  masonry  chambers  (Fig.  112),  care  being  taken  that 
the  temperature  does  not  become  too  elevated.  It  is  largely  em- 


STRONTIUM.  269 

ployed  as  a  bleaching  and  disinfecting  agent,  and  owes  this  prop- 
erty to  the  facility  with  which  it  gives  up  its  chlorine.  It  is 
decomposed  by  very  dilute  acids,  even  by  the  carbon  dioxide  of 
the  air. 

CaCl(ClO)         +        CO2        =        CaCO3        +        Cl2 

When  thrown  into  water,  it  yields  a  solution  containing  calcium 
hypochlorite  and  calcium  chloride. 

2CaCl(C10)        =        CaCl2        +        Ca(ClO)8 
Chlorinated  lime.  Calcium  hypochlorite. 

When  it  is  heated,  or  when  its  solution  is  boiled,  it  is  converted 
into  calcium  chloride  and  calcium  chlorate. 

6CaCl(C10)         =         SCaCl2         +         Ca(C103)2 
Chlorinated  lime.  Calcium  chlorate. 

440.  CALCIUM  CARBIDE,  CaC2,  is  a  compound  produced  when 
a  mixture  of  lime  and  carbon  is  heated  in  the  electric  furnace. 
It  is  a  dark  crystalline  solid,  having  a  density  of  2.2.     It  reacts 
with  water  to  form  calcium  hydroxide  and  acetylene  (see  p.  186). 

441.  TESTS  FOR  CALCIUM. — Solutions  of  calcium  salts  are  not 
affected  by  hydrogen  sulphide.     In  solutions  which  are  not  very 
dilute,  sulphuric  acid  and  the  soluble  sulphates  produce  a  white 
precipitate  of  calcium  sulphate.     Solution  of  oxalic  acid  to  which 
a  few  drops  of  ammonia  have  been  added,  yields  a  white  precipitate 
of  calcium  oxalate,  even  in  the  most  dilute  calcium  solutions.    The 
salts  of  calcium  communicate  a  reddish-yellow  color  to  flame,  and 
the  calcium  spectrum  is  quite  characteristic.  (See  frontispiece.) 

442.  Strontium,  Sr=z87.5. — The  principal  strontium  minerals 
are  the  sulphate,  called  celestite,  on  account  of  the  blue  color  of 
many  specimens,  and  the  carbonate,  called  strontianite.     The  first, 
being  the  more  abundant,  serves  for  the  preparation  of  the  stron- 
tium salts:  it  is  powdered,  and  intimately  mixed  with  charcoal, 
and  the  mixture  heated  to  bright  redness  in  a  covered  crucible. 
Carbon  monoxide  is  then  disengaged,  while  the  sulphate  is  re- 
duced to  the  sulphide,  SrS.     The  gray  mass  containing  this  sul- 
phide is  then  treated  with  the  acid  corresponding  to  the  desired 
salt,  which  separates  in  crystals  when  the  solution  is  evaporated. 


270  LESSONS    IN    CHEMISTRY. 

443.  STRONTIUM    CHLORIDE,  SrCl2  -f-  6H20,  crystallizes  in 
deliquescent  needles.     It  is  moderately  soluble  in  alcohol. 

444.  STRONTIUM  MONOXIDE,  SrO,  is  prepared  by  strongly 
calcining  strontium  nitrate.     It  is  an  infusible,  gray,  porous 
mass :  when  exposed  to  the  air,  it  absorbs  moisture  and  carbon 
dioxide.     By  the  action  of  water,  it  is  converted  into  strontium 
hydroxide,  Sr(OH)2,  which  is  more  soluble  in  water  than  calcium 
hydroxide,  and  crystallizes  with  eight  molecules  of  water.     There 
is  also  a  dioxide,  SrO2. 

445.  TESTS  FOR  STRONTIUM. — Solutions  of  the  ordinary  salts 
of  strontium  are  colorless ;  they  are  not  precipitated  by  hydrogen 
sulphide.     Sodium  carbonate  produces  a  voluminous  white  precip 
itate  of  strontium  carbonate.     Sulphuric  acid  precipitates  stron 
tium  sulphate  in  solutions  not  too  dilute.     The  Bunsen  flame  is 
colored  red  by  strontium  compounds.     The  most  characteristic 
lines  of  the  strontium  spectrum  are  in  the  blue,  red,  and  orange. 

446.  Barium,  Ba  =  137. — Barium  occurs  in  nature  in  heavy - 
sjpar,  which  is  the  sulphate,  and  withcrite,  which  is  the  carbonate. 
The  isolation  of  this  metal  is  an  extremely  difficult  matter: 
small  amounts  have  been  obtained  by  electrolyzing  the  fused 
chloride,  and  by  reducing  the   oxide  in  the  electric  furnace. 
Its  salts  may  be  prepared  by  dissolving  the  native  carbonate  in 
the  corresponding  acid,  or  from  the  sulphate,  which  must  first  be 
reduced  to  sulphide.     The  finely-powdered  sulphate  is  made  into 
a  paste  with  rosin  and  linseed  oil,  and  the  mixture  is  shaped  into 
little  balls  which  are  calcined  in  a  covered  crucible. 

447.  BARIUM  CHLORIDE,  BaCl2,  is  obtained  when  the  sulphide 
is  dissolved  in  hydrochloric  acid,  and  the  filtered  solution  suffi- 
ciently concentrated.     Its  crystals  contain  two  molecules  of  water. 
They  are  soluble  in  rather  more  than  twice  their  weight  of  cold 
water,  in  much  less  boiling  water,  and   also  slightly  soluble  in 
alcohol.     Barium  chloride  is  the  reagent  generally  used  for  the 
detection  of  sulphuric  acid. 

448.  BARIUM  MONOXIDE,  BaO,  often  called  baryta,  is  prepared, 
like  strontium  monoxide,  by  calcining  the  nitrate.    It  forms  a  gray, 
porous  mass,  which  absorbs  moisture  and  carbon  dioxide  from  the 


BARIUM.  271 

air.  If  a  fragment  of  this  substance  be  sprinkled  with  a  few 
drops  of  water,  barium  hydroxide  is  formed  with  such  energy  that 
the  mass  sometimes  becomes  red  hot. 

449.  BARIUM  HYDROXIDE,  Ba(OH)2,  is  made  by  dissolving  the 
oxide  in  boiling  water,  which  dissolves  about  one-tenth  its  weight. 
When  the  liquid  cools,  the  greater  part  of  the  hydroxide  is  deposited 
in  colorless  crystals  which  contain  Ba(OH)2  +  8H20.    The  solu- 
tion, called  baryta-water,  is  used  in  testing  for  carbon  dioxide. 

450.  BARIUM  DIOXIDE,  BaO2. — At  a  dull  red  heat,  barium 
monoxide  will  absorb  oxygen,  and  become  converted  into  the  di- 
oxide, which  is  made  by  passing  oxygen  over  the  monoxide  .heated 
in  a  porcelain  tube  or  in  a  crucible.     Barium  dioxide  is  a  grayish- 
white  substance,  which,  when  thrown  into  water,  crumbles  to  a 
white  hydroxide.     It  loses  one  atom  of  oxygen  at  a  bright  red  heat, 
and  the  monoxide  remains.     By  the  action  of  strong  sulphuric 
acid,  barium  dioxide  is  converted  into  barium  sulphate,  while  ozone 
is  disengaged.    With  hydrochloric  acid,  the  hydrated  dioxide  yields 
barium  chloride  and  hydrogen  dioxide. 

451.  TESTS  FOR  BARIUM. — Hydrogen  sulphide  occasions  no 
precipitate  in  solutions  of  barium  salts.     Sodium  carbonate  throws 
down  white  barium  carbonate.     Sulphuric  acid  precipitates  insol- 
uble barium  sulphate,  even  in  exceedingly  dilute  solutions,  and 
the  precipitate  is  insoluble  in  nitric  acid,  either  cold  or  boiling. 
Barium  salts  communicate  a  green  color  to  flames.     Among  the 
numerous  lines  of  the  barium  spectrum,  two  bright  green  ones 
are  most  prominent  (see  frontispiece). 

The  barium  salts  are  very  poisonous. 

452.  The  nitrates  of  barium  and  strontium  are  employed  in  pyrotechny,  for 
they  impart  to  fireworks  the  characteristic  flame  colors  of  the  metals. 

A  red  fire  may  be  made  by  mixing  30  parts  of  potassium  chlorate,  17  parts 
of  sulphur,  2  of  charcoal,  and  45  of  strontium  nitrate.  The  materials  must 
be  pulverized  separately,  and  may  be  mixed  by  repeated  passing  through  a 
sieve.  A  green  fire  may  be  made  by  similarly  mixing  33  parts  of  potassium 
chlorate,  10  of  sulphur,  5  of  charcoal,  and  52  of  barium  nitrate.  If  it  be 
desired  that  the  fires  shall  produce  little  or  no  smoke,  the  following  formulae 
may  be  used;  the  ammonium  picrate  may  be  made  by  adding  ammonia- 
water  to  a  concentrated  alcoholic  solution  of  picric  acid,  until  the  liquid  has 
an  ammoniacal  odor,  and  then  collecting  and  carefully  drying  the  precipitate. 


272  LESSONS    IN    CHEMISTRY. 

Ammonium  Ferrous  Strontium  Barium 

picrate.  picrate.  nitrate.  nitrate. 

Yellow      ......       *0  50 

Green 48  ...  ...  52 

Red 54  ...  46 

The  stars  for  rockets  and  Roman  candles  are  made  by  moistening  the  colored 
fires  and  forming  them  into  small  balls;  these  are  dried  and  introduced  into 
the  tube,  from  which  they  are  projected  by  a  small  charge  of  gunpowder. 


LESSON    LII. 

LEAD.     Pb  =  207. 

453.  In  many  of  its  chemical  relations,  lead  resembles  calcium,  strontium, 
and  barium,  and  it  might  be  classed  in  the  same  group  of  metals ;  but  in  a 
number  of  its  compounds  it  acts  as  a  tetratomic  element.  It  forms  a  dioxide, 
PbO2,  and  a  tetrachloride,  PbCl4.  In  the  dioxides  of  strontium  and  barium, 
it  is  not  probable  that  the  atoms  of  these  metals  are  tetratomic :  it  appears 
rather  that  the  two  atoms  of  oxygen  are  related  to  each  other,  while  each  is 
also  related  to  the  atom  of  metal.  In  lead  dioxide  the  lead  atom  is  tetratomic. 

454.  The  principal  lead  ores  are  galena,  which  is  lead  sulphide, 
and  cerussite,  which  is  the  carbonate.  The  reduction  of  the  latter 
mineral  is  an  exceedingly  simple  process  :  it  is  heated  with  char- 
coal ;  the  reduced  lead  collects  on  the  hearth  of  the  furnace,  and 
is  drawn  off  as  it  accumulates. 

Galena  may  be  reduced  by  heating  it  with  scrap  iron :  iron 
sulphide  and  lead  are  formed,  and,  the  lead  being  the  heavier,  the 
iron  sulphide  floats  on  the  surface  and  is  drawn  off  as  slag.  The 
more  usual  process,  known  as  the  reaction  process,  consists  in 
heating  the  galena  ou  the  hearth  of  a  reverberatory  furnace  (Fig. 
112)  provided  with  openings  (D.)  for  the  admission  of  air.  Part 
of  the  lead  sulphide  is  so  converted  into  oxide,  and  another  portion 
into  sulphate.  When  this  reaction  has  sufficiently  advanced,  the 
openings  of  the  furnace  are  closed,  and  the  heat  is  increased. 
Under  these  circumstances  the  unaltered  sulphide  reacts  with  both 
oxide  and  sulphate,  metallic  lead  being  formed,  while  sulphur 
dioxide  is  disengaged. 

PbS     +    2PbO      =    3Pb    +    SO* 
PbS    +     PbSO*    =     2Pb    +    2SOa 


LEAD.  273 

Sometimes  charcoal  powder  is  added  after  the  air-openings  are 
closed,  in  order  to  aid  in  the  reduction  of  the  oxide  and  sulphate. 


•  •••  •     .          '        .        -i.     :g^BMg"g»lia-J»JlxV 

FIG.  112. 

Lead  is  a  bluish -white  metal,  having  a  brilliant  lustre,  which 
soon  tarnishes  by  exposure  to  air.  It  is  soft,  and  can  be  scratched 
by  the  finger-nail :  it  is  quite  malleable,  but  has  so  little  tenacity 
that  it  cannot  readily  be  drawn  into  wire.  Its  density  is  about 
11.36  :  it  melts  at  about  334°.  It  may  be  crystallized  by  allow- 
ing a  crucible  full  of  the  molten  metal  to  cool  until  a  crust  forms 
on  its  surface,  piercing  the  crust,  and  pouring  out  the  still  liquid 
interior.  The  interior  of  the  crucible  is  then  found  to  be  lined 
with  octahedral  crystals.  Molten  lead  absorbs  oxygen  from  the 
air,  and  its  surface  becomes  covered  with  a  film  of  lead  oxide,  PbO. 

Lead  is  only  slightly  attacked  by  hydrochloric  acid,  and  is 
scarcely  affected  by  dilute  sulphuric  acid.  Strong  sulphuric 
acid  dissolves  it  by  the  aid  of  heat,  sulphur  dioxide  being  given 
off.  Nitric  acid  converts  it  into  lead  nitrate,  and  disengages 
red  vapors.  As  the  nitrate  is  almost  insoluble  in  nitric  acid, 
the  latter  should  be  diluted  with  water. 

Pure  water  containing  dissolved  air  and  carbon  dioxide  dissolves 
a  small  quantity  of  lead  in  the  form  of  hydrate  and  carbonate,  and 
for  this  reason  lead  is  an  unsafe  metal  for  lining  rain-water  cisterns 
intended  for  storing  drinking-water.  Most  spring-  and  river-waters 

18 


274  LESSONS    IN   CHEMISTRY. 

contain  small  quantities  of  sulphates :  when  such  water  flows 
through  lead  pipes,  the  surface  of  the  metal  becomes  quickly  cov- 
ered with  a  film  of  insoluble  lead  sulphate,  which  protects  the 
pipe  from  further  action,  and  the  water  from  being  poisoned  by 
the  introduction  of  lead  compounds. 

Lead,  and  all  its  soluble  compounds,  as  well  as  such  as  may  be  rendered 
soluble  by  the  juices  of  the  stomach,  are  poisonous,  and  the  poisonous  effects 
are  cumulative.  Workmen  employed  in  the  manufacture  of  white  lead,  red 
lead,  and  other  lead  compounds,  frequently  suffer  from  chronic  lead-poisoning, 
as  do  also  painters  and  color-grinders.  Small  quantities  of  lead  are  then  accu- 
mulated in  the  system,  and  cause  peculiar  disorders,  among  which  lead  colic 
is  the  most  common :  one  of  the  characteristic  symptoms  of  lead-poisoning  is 
a  peculiar  blue  line  around  the  borders  of  the  gums.  The  workmen  in  lead- 
works  usually  drink  small  quantities  of  an  exceedingly  dilute  sulphuric  acid, 
by  which  the  lead  in  the  system  is  converted  into  the  insoluble  and  innocuous 
sulphate.  In  cases  of  chronic  lead-poisoning,  the  administration  of  potassium 
iodide  removes  the  metal  from  the  tissues  by  the  formation  of  lead  iodide, 
which  is  soluble  in  solutions  of  potassium  iodide,  and  can  consequently  be 
eliminated  by  the  excretory  organs. 

Metallic  lead  is  used  in  the  form  of  sheets  for  roofing  and  lining 
tanks  ;  it  is  manufactured  into  lead  pipe  ;  type  metal,  which  is  80 
per  cent,  lead  and  20  per  cent,  antimony ;  pewter,  which  contains 
between  eighty  and  ninety  per  cent,  tin,  the  remainder  being  lead ; 
and  plumbers'  solder,  an  alloy  of  lead  and  tin.  Enormous  quantities 
of  lead  are  employed  for  the  manufacture  of  shot,  which  is  made 
by  allowing  the  molten  metal  to  run  through  a  sieve,  and  the  drops 
to  fall  from  a  height  into  water.  In  common  qualities  of  tin  plate, 
a  large  proportion  of  the  coating1  is  lead  instead  of  pure  tin. 

455.  LEAD    CHLORIDE,  PbCP,  is   prepared   by  boiling  lead 
oxide  in  hydrochloric  acid,  and  is  precipitated  when  hydrochloric 
acid  or  a  soluble  chloride  is  added  to  the  solution  of  a  lead  salt. 
It  is  a  white  solid,  only  slightly  soluble  in  cold  water,  but  dis- 
solving in  thirty-three  times  its  weight  of  boiling  water :  when 
the  hot  solution  cools,  the  chloride  separates  in  brilliant  anhydrous 
needles.     It  is  employed  in  the  manufacture  of  several  yellow 
colors,  which  are  oxy chlorides  of  lead,  or  mixtures  of  the  chloride 
and  oxide. 

456.  LEAD  IODIDE,  Pbl2,  is  deposited  as  a  yellow  precipitate 
when  potassium  iodide  is  added  to  the  solution  of  a  lead  salt.     It 


LEAD    OXIDES.  275 

is  almost  insoluble  in  cold  water,  but  dissolves  in  a  little  less  than 
two  hundred  times  its  weight  of  boiling  water,  from  which  it 
separates  on  cooling  in  beautiful  golden-yellow  scales. 

457.  LEAD  MONOXIDE,  PbO. — This  body  is  produced  by  the 
direct  oxidation  of  melted  lead  by  the  air.    It  is  an  accessory  prod- 
uct in  the  cupellation  of  lead  for  the  extraction  of  silver  (§  426). 
It  is  known  in  commerce  by  the  names  massicot  and  litharge : 
massicot  is  a  yellow,  amorphous  powder ;  by  fusing  this  powder 
and  pulverizing  the  resulting  mass,  litharge  is  obtained  as  reddish- 
yellow,  crystalline  scales.     Lead  monoxide  is  slightly  soluble  in 
water,  and  will  restore  the  blue  color  to  reddened  litmus.    It  melts 
at  a  red  heat,  but  cannot  be  melted  in  vessels  of  glass,  porcelain, 
or  clay,  because  it  combines  with  silica  and  forms  a  very  fusible 
silicate,  so  destroying  the  vessel.     It  is  readily  reduced  by  char- 
coal and  by  hydrogen.     It  is  used  in  the  manufacture  of  the  salts 
of  lead :  when  it  is  boiled  with  linseed  oil,  the  latter  acquires  the 
property  of  quickly  drying  or  hardening  when  exposed  to  the  air. 

When  the  solution  of  a  lead  salt  is  treated  with  an  alkaline 
hydroxide,  lead  hydroxide,  Pb(OH)2,  is  thrown  down  as  a  white 
precipitate,  soluble  in  an  excess  of  the  alkaline  hydroxide. 

458.  LEAD  DIOXIDE,  PbO2,  is  obtained  by  treating  red  lead 
with  nitric  acid.     Red  lead  is  a  combination  of  the  monoxide  and 
dioxide,  and  the  nitric  acid  dissolves  out  the  monoxide,  forming 
lead  nitrate,  which  is  soluble  and  can  be  washed  out,  while  the 
dioxide  remains  as  a  brown  powder.      It  is  not  soluble  in  water, 
and  by  the  action  of  heat  is  decomposed  into  lead  monoxide  and 
oxygen.     It  is  a  very  energetic  oxidizing  agent :  a  little  sulphur 
may  be  ignited  by  rubbing  it  in  a  mortar  with  some  lead  dioxide. 
It  absorbs  sulphur  dioxide,  forming  lead  sulphate  ;  with  hydro^ 
chloric  acid  it  forms  lead  chloride  and  water,  while  chlorine  is  dis- 
engaged. 

PbO2     +     4HC1    =     PbCl2     +     2H20     +     Cl2 

459.  RED    LEAD,    (PbO)2Pb02.— This  body  is  prepared  by 
heating  massicot  to  300°  in  furnaces  so  arranged  that  it  is  freely 
exposed  to  a  current  of  air ;  oxygen  is  then  absorbed,  and  a  beau- 
tiful red  powder,  called  minium,  or  red  lead,  is  formed.     It  is 


276  LESSONS   IN    CHEMISTRY. 

plumboso-plumbic  oxide,  but  the  proportions  of  the  monoxide 
and  dioxide  which  it  contains  are  not  constant,  though  usually 
responding  to  the  formula  given.  When  heated,  its  color  darkens  ; 
at  a  red  heat  it  loses  part  of  its  oxygen  and  is  converted  into 
the  monoxide.  Red  lead  is  employed  as  a  pigment,  and  in  the 
manufacture  of  flint-glass,  of  which  the  brilliancy  and  refractive 
power  are  due  to  silicate  of  lead.  Mixed  into  a  paste  with  linseed 
oil,  it  forms  an  excellent  cement. 

460.  LEAD  SULPHIDE,  PbS. — This  compound  is  the  mineral 
galena,  which  is  found  in  cubical  crystals  of  a  bluish-gray  color 
and  metallic  appearance.     Its  density  is  7.58 ;  it  is  much  harder 
than  lead,  and  rather  brittle.     It  melts  when  heated  to  redness, 
and  in  contact  with  air  is  then  oxidized  to  oxide  and  sulphate. 
It  is  converted  into  lead  chloride  by  boiling  with  hydrochloric 
acid,  hydrogen  sulphide  being  disengaged.     Boiling  nitric  acid 
converts  it  into  lead  sulphate. 

461.  TESTS  FOR  LEAD. — With  the  exception  of  the  nitrate 
and  acetate,  none  of  the  more  common  lead  salts  are  very  soluble. 
Those  which  are  soluble  have  a  sweet  and  somewhat  astringent 
taste.     Hydrogen  sulphide  forms  in  them  a  black  precipitate  of 
lead  sulphide  :  potassium  and  sodium  hydroxides  and  ammonia  pro- 
duce white  precipitates,  which  are  soluble  in  an  excess  of  either 
of  the  first  two  reagents.     Sulphuric  acid  yields  a  white  precipi- 
tate even  in  the  most  dilute  solutions.    Hydrochloric  acid  throws 
down  white  lead  chloride,  unless  the  solution  be  too  dilute  ;  this 
precipitate  is  dissolved  by  boiling,  and,  on  cooling  again,  sepa- 
rates in  crystals.      Potassium  chromate  precipitates  yellow  lead 
chromate,  which  is  soluble  in  the  alkaline  hydroxides. 

If  a  salt  of  lead  be  mixed  with  sodium  carbonate,  and  heated 
on  a  piece  of  charcoal  in  the  inner  flame  of  a  blow-pipe,  a  small 
bead  of  metallic  lead  is  obtained,  and  the  softness  of  the  bead 
indicates  the  nature  of  the  metal. 


MAGNESIUM.  277 

LESSQN    LIIL 
MAGNESIUM.— ZINC.— CADMIUM. 

462.  These  three  metals  form  a  natural  group,  to  which  belongs  also  a 
fourth,  glucinum,  of  which  the  silicate  constitutes  part  of  the  mineral  beryl 
and  the  green  precious  stone  emerald.  They  are  diatomic  metals. 

463.  Magnesium,  Mg  =  24. — This  element  occurs  in  nature 
as  carbonate  in  the  mineral  magnesite,  as  sulphate  in  kieserite,  and 
as  silicate  in  serpentine  and  soapstone.     The  metal  is  obtained  by 
heating  its  chloride  with  sodium  in  an  iron  crucible,  a  mixture  of 
common  salt  and  calcium  fluoride  being  added  as  a  flux.     The  so- 
dium is  converted  into  sodium  chloride,  and  the  magnesium  sepa- 
rates in  little  globules  diffused  through  the  molten  mixture,  which 
is  constantly  stirred.     When  perfectly  cold,  the  mass  is  broken  up, 
and  the  globules  of  magnesium  are  removed  and  the  metal  puri- 
fied by  distillation  in  a  current  of  hydrogen.     It  is  now  manu- 
factured by  decomposing  fused  carnallite,  MgCP.KCl,  by  an 
electric  current. 

Magnesium  is  a  bluish-white  metal ;  its  surface,  which  is  not 
very  brilliant,  soon  tarnishes  in  the  air.  Its  density  is  about 
1.75.  It  is  both  ductile  and  malleable,  and  is  ordinarily  rolled 
into  ribbon  or  drawn  into  wire.  It  does  not  decompose  water  at 
ordinary  temperatures,  but  it  acts  slightly  at  the  temperature  of 
boiling.  It  melts  at  500°,  and  if  exposed  to  the  air  takes  fire 
and  burns  with  great  brilliancy.  The  light  of  burning  mag- 
nesium is  very  bright,  and  lamps  are  constructed  in  which  the 
ribbon  is  gradually  supplied  by  clock-work.  Such  lamps  are  em- 
ployed in  photographing  the  interior  of  caves  and  other  dark 
localities.  The  product  of  the  combustion  is  magnesium  oxide 
MgO.  Magnesium  combines  directly  with  nitrogen. 

464.  MAGNESIUM  CHLORIDE,  MgCP. — When  magnesium  or 
its  oxide  or  carbonate  is  dissolved  in  hydrochloric  acid,  and  the 
solution  is  concentrated,  crystals  of  magnesium  chloride,  with  six 
molecules  of  water  of  crystallization,  are  obtained.     These  crystals 


278  LESSONS   IN    CHEMISTRY. 

cannot  be  rendered  anhydrous,  and  their  solution  cannot  be  evap- 
orated to  dryness,  for  they  decompose  into  hydrochloric  acid  and 
magnesium  oxide. 

MgCl*        +        H2Q        =        MgO        +        2HC1 

Anhydrous  magnesium  chloride  is  prepared  by  dissolving  the 
oxide  or  carbonate  in  hydrochloric  acid,  and  adding  two  molecules 
of  ammonium  chloride  for  every  atom  of  magnesium.  This  so- 
lution may  be  evaporated  to  dryness,  and  leaves  an  anhydrous 
double  chloride  of  magnesium  and  ammonium.  The  double  salt 
is  heated  in  a  clay  crucible  until  all  of  the  ammonium  chloride  is 
driven  off,  while  the  magnesium  chloride  remains  in  a  state  of 
fusion  ;  on  cooling,  it  solidifies  to  a  pearly-white  mass.  In  this 
form  it  is  used  for  the  manufacture  of  magnesium.  It  is  very 
soluble  in  water,  but  from  the  solution  only  the  hydrated  crystals 
can  be  obtained. 

465.  MAGNESIUM  OXIDE,  MgO. — This  is  the  calcined  mag- 
nesia of  the  pharmacies.    It  is  made  by  calcining  magnesium 
carbonate,  or  the  mixture  of  hydrate  and  carbonate  commonly 
called  magnesia  alba.     It  is  a  tasteless  white  powder,  infusible 
except  in  the  electric  furnace.    It  is  insoluble  in  water,  but  com- 
bines with  that  liquid,  forming  magnesium  hydroxide,  Mg(OH)2,  a 
substance  which  restores  the  blue  color  to  reddened  litmus.     This 
same  hydrate  is  precipitated  when  an  alkaline  hydroxide  is  added 
to  the  solution  of  a  magnesium  salt. 

466.  TESTS  FOR  MAGNESIUM. — Neither  hydrogen  sulphide  nor 
ammonium  sulphide  occasions  any  precipitate  in  magnesium  solu- 
tions.    Sodium  carbonate  throws  down  a  white,  flocculent  precipi- 
tate of  the  hydrated  carbonate,  which  when  dried  in  the  air  con- 
stitutes white  magnesia.     Potassium  and  sodium  hydroxides  yield 
white  precipitates  of  the  hydroxide,  as  does  also  ammonia  unless 
the  solution  be  acid  or  contain  ammonium  chloride.     Sodium  phos- 
phate with  a  few  drops  of  ammonia  produces  a  white,  crystalline 
precipitate  of  magnesium  ammonium  phosphate,  Mg(NH*)P04. 

467.  Zinc,  Zn  =  65. — The  ores  from  which  zinc  is  obtained  are 
the  carbonate,  which  is  called  smithsonite,  and  the  sulphide,  called 
blende.     These  minerals  are  broken  up  and  roasted  in  furnaces 


ZINC. 


279 


much  resembling  lime-kilns.  At  the  temperature  of  the  roast- 
ing, which  is  a  dull  red  heat,  the  carbonate  loses  carbon  dioxide 
and  the  water  which  it  usually  contains,  and  is  converted  into  zinc 
oxide :  the  sulphide  is  also  oxidized  by  roasting,  sulphur  dioxide 
being  disengaged.  The  zinc  oxide  so  obtained  is  mixed  with  char- 
coal and  heated  for  about  twenty-four  hours  to  a  high  temperature 
in  clay  or  iron  vessels :  carbon  monoxide  is  disengaged,  while  the 
zinc  volatilizes  and  is  condensed  in  suitable  apparatus.  Various 
processes  of  distillation  are  employed :  we  need  only  consider  the 
two  which  are  generally  used.  In  the  Belgian  process,  the  mix- 
ture of  zinc  oxide  and  charcoal  is  introduced  into  clay  tuhes,  closed 
at  one  end,  and  inserted  in  an  inclined  position  in  the  walls  of  the 
furnace ;  to  the  open  and  exterior  end  of  each  tube  is  adapted  a 
bulged  pipe,  in  which  the  zinc  vapor  condenses  and  the  metal  col- 
lects. In  order  that  no  air  may  enter  the  tubes  and  oxidize  the 
zinc,  a  sheet-iron  noz- 
zle, having  a  hole  for 
the  exit  of  the  gases, 
is  passed  over  the  ex- 
tremity of  this  con- 
denser (Fig.  114). 
The  tubes  are  usu- 
ally about  a  metre  in 
length,  and  twenty 
centimetres  in  inte- 
rior diameter.  A  large  number  of  them  are  placed  in  parallel 
rows  in  the  same  furnace:  when  all  the  zinc  has  distilled,  the 
receivers  containing  it  are  removed,  and  a  fresh  charge  of  roasted 
ore  and  charcoal  is  introduced  into  the  tubes. 

In  the  Silesian  process,  the  retorts  are  arched,  and  very  similar 
in  form  to  those  employed  in  the  manufacture  of  illuminating  gas 
from  coal. 

468.  At  present,  the  furnace  used  in  the  reduction  of  zinc  by  both  the  Bel- 
gian and  Silesian  methods  is  that  known  as  the  Siemens  regenerative  furnace, 
which  effects  a  great  saving  of  fuel.  In  this  arrangement,  the  coal  is  fed  grad- 
ually to  the  grate  of  a  peculiar  fire-box,  called  the  generator,  and  the  admis- 
sion of  air  is  there  so  regulated  that  as  much  carbon  monoxide  as  possible  may 


FIG.  114. 


280 


LESSONS   IN   CHEMISTRY. 


be  produced  by  an  imperfect  combustion ;  in  addition,  the  ashes  below  the 
grate  are  kept  moist,  and  the  steam  passing  into  the  fire  reacts  with  the  hot 
carbon,  producing  hydrogen  and  carbon  monoxide  (§  232) ;  the  highly-heated 
gas  is  led  through  a  chamber  filled  with  fire-bricks,  which  become  very  hot; 
by  a  system  of  dampers,  the  gases  are  then  directed  through  another  similar 
chamber,  while  air  is  admitted  to  that  which  has  been  heated ;  the  heated  air 
from  the  one,  and  the  heated  gas  from  the  other,  are  then  brought  in  contact 
where  it  is  desired  that  the  greatest  temperature  shall  be  produced  by  the  per- 
fect combustion  of  the  gases.  The  heat  of  the  waste  products  of  combustion 
is  applied  to  heating  other  fire-brick  chambers,  which  will  afterwards  serve  for 

the  admission  of 
air,  as  these  regen- 
erators, as  they  are 
called,  are  cooled 
by  the  entering 
air.  Figure  115 
represents  the  fire- 
brick chambers  of 
a  Siemens  furnace 
applied  to  the  Si- 
lesian  zinc  process. 
The  two  chambers 
on  each  side  serve 
alternately,  one 
for  the  entrance 
of  air,  and  one  for 
the  gas  from  the 
generator,  while 
the  other  two  serve 
for  the  exit  of  the 
products  of  com- 
bustion. The 
heated  air  and  gas 
from  A  and  A' 
come  in  contact  in 

the  space  B,  and  the  flames  play  through  openings  in  the  floor  above  which 
are  the  clay  retorts.  The  heated  products  of  combustion  pass  over  the  retorts 
in  another  similar  chamber,  C,  and  from  above  downwards  through  other  fire- 
brick chambers,  D  and  D'.  The  dampers  allow  the  direction  of  the  current  of 
gas  and  air  to  be  reversed  from  A  A'  to  D  D'  as  often  as  necessary,  and  in 
practice  it  is  so  changed  about  once  every  hour. 

Zinc  must  usually  be  purified  before  it  is  sent  into  commerce, 
and  the  most  harmful  impurity  is  lead,  for  it  impairs  the  mallea- 
bility of  the  zinc.  The  lead  is  separated  in  great  part  by  melting 


FIG.  115. 


ZINC.  281 

the  zinc  in  moulds  which  are  slightly  inclined  and  have  a  cavity  at 
the  lower  end :  in  this  the  greater  part  of  the  lead  collects  by 
reason  of  its  greater  density,  and  may  be  broken  from  the  cooled 
ingot.  Commercial  zinc  usually  contains  small  quantities  of  iron, 
copper,  lead,  cadmium,  and  sometimes  arsenic.  Sheet  zinc  is  the 
purest. 

Zinc  is  a  bluish-white  metal,  capable  of  taking  a  high  lustre. 
Its  density  varies  from  6.86,  that  of  the  cast  metal,  to  7,  that  of 
the  rolled.  Pure  zinc  may  be  hammered  into  sheets,  or  drawn 
into  wire  at  ordinary  temperatures,  but  commercial  zinc  must  be 
rolled  at  about  150°.  It  again  becomes  brittle  at  200°, 'and  may 
readily  be  pulverized  in  a  mortar  heated  to  that  temperature.  It 
melts  at  410°,  and  distils  at  about  1000°.  It  is  unaltered  by  dry 
air,  but  in  moist  air  its  surface  becomes  dull  from  the  formation 
of  a  film  of  hydrated  carbonate,  which  protects  the  metal  from 
further  action. 

When  it  is  heated  to  redness  in  the  air,  it  takes  fire  and  burns 
with  a  bluish  flame,  giving  off  clouds  of  white  zinc  oxide,  ZnO. 
Fine  zinc  shavings  may  be  lighted  by  a  match,  and  burn  brilliantly 
in  the  air.  If  some  zinc  be  heated  to  redness  in  a  ladle  or  cruci- 
ble, and  pieces  of  potassium  nitrate  be  thrown  in,  the  oxygen  of 
the  decomposing  nitre  energetically  oxidizes  the  metal. 

Zinc  is  dissolved  by  hydrochloric,  sulphuric,  and  nitric  acids, 
and  by  boiling  solutions  of  potassium  and  sodium  hydroxides.  In 
the  latter  case,  hydrogen  is  disengaged  and  an  alkaline  zincate  is 
formed,  a  compound  in  which  zinc  oxide  appears  to  act  as  an  acid 
radical.  We  have  already  studied  the  action  of  the  acids  on  zinc. 

Zinc  is  employed  in  the  manufacture  of  galvanized  iron,  which 
is  made  by  dipping  carefully  cleaned  iron  objects  into  melted  zinc ; 
brass,  which  is  an  alloy  of  copper  and  zinc ;  the  plates  of  voltaic 
batteries ;  and  for  the  preparation  of  zinc  white,  which  is  zinc 
oxide. 

469.  ZINC  CHLORIDE,  ZnCl2,  may  be  formed  by  the  direct 
union  of  zinc  and  chlorine,  a  union  which  takes  place  brilliantly 
when  fine  zinc  shavings  are  thrown  into  a  jar  of  chlorine.  It  is 
prepared  by  dissolving  zinc  in  hydrochloric  acid.  It  forms  deli- 


282  LESSONS   IN    CHEMISTRY. 

quescent  crystals  containing  one  molecule  of  water  of  crystalliza- 
tion, which  is  expelled  by  heat,  and  the  anhydrous  salt  fuses  at 
250°.  The  latter  is  very  deliquescent,  and  is  an  energetic  dehy- 
drating agent.  It  is  employed  as  a  caustic  in  surgery.  Zinc 
chloride  is  very  soluble  in  water,  and  its  solution,  to  which  a  little 
free  hydrochloric  acid  and  some  ammonium  chloride  have  been 
added,  is  an  excellent  soldering  liquid,  for  moistening  the  surface 
of  iron,  zinc,  copper,  and  brass  articles  before  soldering. 

470.  ZINC  OXIDE,  ZnO,  is  prepared  on  a  large  scale  by  heating 
zinc  in  large  muffles  in  which  its  vapor  may  come  freely  in  con- 
tact with  air.     The  product  is  stirred  up  with  water ;  the  heavier 
particles  of  unaltered  zinc  sink  to  the  bottom,  while  the  zinc  oxide 
remains  suspended  in  the  creamy  liquid  which  is  rapidly  poured 
off  and  allowed  to  settle.     The  separation  of  fine  powders  by  this 
method  is  called  elutriation. 

Zinc  oxide  is  a  white  powder,  insoluble  in  water.  It  is  em- 
ployed as  a  substitute  for  white  lead  in  painting  localities  exposed 
to  hydrogen  sulphide,  which  would  blacken  a  lead  pigment. 

When  an  alkaline  hydroxide  is  added  to  the  solution  of  a  zinc 
salt,  zinc  hydroxide,  Zn(OH)2,  is  thrown  down  as  a  white  precipitate. 

ZnSO*     +     2KOH     =     K'SO4     +     Zn(OH)2 
This  precipitate  is  soluble  in  an  excess  of  the  alkaline  hydroxide. 

471.  ZINC  SULPHIDE,  ZnS. — This  compound  is  found  native 
as  zinc  blende,  a  mineral  usually  having  a  more  or  less  intense 
brown  color,  due  to  the  presence  of  a  certain  proportion  of  iron. 
When  ammonium  sulphide  is  added  to  the  perfectly  neutral  solu- 
tion of  a  zinc  salt,  a  white  precipitate  of  hydrated  zinc  sulphide  is 
formed. 

472.  TESTS  FOR  ZINC. — Neutral  solutions  of  zinc   salts   are 
precipitated  white  by  hydrogen  sulphide ;   the  precipitate  is  not 
formed  if  free  mineral  acid   be  present.      Ammonium  sulphide 
produces  a  characteristic  white  precipitate  of  zinc  sulphide.     The 
alkaline  hydroxides  and  ammonia-water  yield  white  zinc  hydrate, 
soluble   in   an   excess   of  the  reagent.       Potassium   ferrocyanide 
throws  down  a  white  precipitate  of  zinc  ferrocyanide.     The  salts 
of  zinc  are  poisonous. 


CADMIUM.  283 

473.  Cadmium,  Cd  =  112. — This  metal  occurs  associated  with  zinc  in  both 
blende  and  calarnine.     It  is  reduced  with  the  zinc,  and,  being  more  volatile 
than  the  latter,  distils  during  the  early  part  of  the  operation.     During  the 
first  few  hours  of  the  reduction  of  many  zinc  ores,  a  brown  powder,  called 
cadmies,  collects  in  the  receivers  attached  to  the  retorts.    This  dust  contains  a 
large  proportion  of  cadmium  oxide,  and  when  distilled  with  charcoal  powder 
yields  an  alloy  of  zinc  and  cadmium.     The  latter  metal  is  purified  by  dis- 
solving the  alloy  in  dilute  sulphuric  acid,  precipitating  cadmium  sulphide  by 
passing  hydrogen  sulphide  through  the  acid  liquid,  dissolving  the  sulphide  in 
hydrochloric  acid,  and  adding  ammonium  carbonate.     Cadmium  carbonate  is 
precipitated ;  this  is  collected,  dried,  and  roasted,  and  the  cadmium  oxide  ob- 
tained is  distilled  with  charcoal  powder. 

Cadmium  has  a  white  color  and  a  brilliant  lustre,  which  soon  becbmes  dull 
in  moist  air.  Its  density  is  8.60.  It  melts  at  320°  and  boils  at  860°.  Hydro- 
chloric and  sulphuric  acids  dissolve  it  rapidly,  disengaging  hydrogen. 

474.  CADMIUM  IODIDE,   CdP,  is  made  by  digesting  cadmium  filings  and 
iodine  in  water.     On  evaporating  the  solution,  beautiful  transparent  and  col- 
orless hexagonal  prisms  of  cadmium  iodide  are  deposited.     It  is  used  in  pho- 
tography. 

475.  CADMIUM  OXIDE,  CdO,  is  obtained  as  a  yellowish-brown  powder  by 
roasting  either  cadmium  nitrate  or  cadmium  carbonate.     It  is  reduced  by  hy- 
drogen and  carbon  at  lower  temperatures  than  those  required  for  the  corre- 
sponding reductions  of  zinc  oxide. 

476.  CADMIUM  SULPHIDE,  CdS,  is  found  in  nature  as  greenockite  in  brilliant 
yellow,  hexagonal  prisms.     It  is  precipitated  as  an  amorphous  yellow  powder 
by  the  action  of  hydrogen  sulphide  on  solutions  of  cadmium  salts.     It  is  em- 
ployed as  a  pigment  by  artists. 

477.  TESTS  FOR  CADMIUM. — Potassium  and  sodium  hydroxides  and  ammonia- 
water  give  white  precipitates  of  cadmium  hydroxide ;  only  that  formed  by  am- 
monia is  soluble  in  an  excess  of  the  reagent.     Hydrogen   sulphide  throws 
down  a  characteristic  yellow  precipitate  of  cadmium  sulphide,  even  in  acid 
solutions.      Potassium  ferrocyanide   gives   a  yellowish-white  precipitate  of 
cadmium  ferrocyanide. 


LESSON    LIV. 

COPPER.    Cu  =  63.1. 

478.  Large  deposits  of  metallic  copper  exist  on  the  shores  of 
Lake  Superior,  the  metal  being  sometimes  found  in  crystals,  some- 
times in  irregular  and  grotesque  masses.  The  more  common 


284 


LESSONS    IN    CHEMISTRY. 


copper  ores  are  cuprous  sulphide,  called  chalcocite,  and  copper 
pyrites,  a  compound  of  cuprous  sulphide  and  iron  sulphide. 
This  metal  is  also  found  as  cuprous  oxide,  cupric  oxide,  and  cupric 
carbonate. 

Pure  copper  ores — those  containing  only  the  oxide,  carbonate, 
or  sulphide  of  copper,  and  very  little  of  other  metals — are  easily 
reduced :  the  sulphide  is  first  converted  into  oxide  by  roasting, 
and  the  ores  are  then  heated  with  charcoal  in  a  somewhat  con- 
ical furnace.  The  reduction  of  copper  pyrites  is  more  difficult, 
especially  if,  as  is  often  the  case,  this  mineral  be  mixed  with  the 
sulphides  of  antimony,  arsenic,  zinc,  etc.  If  such  ore  contains  a 
large  proportion  of  copper,  it  may  be  worked  by  a  dry  process ;  but 
if  only  a  small  percentage  of  copper  is  present,  a  method  of  solu- 
tion is  adopted.  In  the  dry  process,  the  ore  is  first  roasted  by 
being  fed  from  hoppers  on  to  the  hearth  of  a  reverberatory  fur- 
nace (Fig.  116),  where  it  is  swept  by  the  flame  of  a  fire.  Part  of 


FIG.  116. 

the  sulphur  is  so  converted  into  sulphurous  oxide,  which  may  be 
used  for  the  manufacture  of  sulphuric  acid,  while  the  iron  and 
copper  of  the  pyrites  are  partially  converted  into  oxide  and  sul- 
phate. A  quantity  of  sand  and  silicate  of  iron  from  a  subsequent 
stage  of  the  operation  is  then  added,  and  the  mass  is  transferred 
either  to  rotating  cylindrical  furnaces  or  to  reverberatory  furnaces 
with  deep  hearths,  where  it  can  be  strongly  heated.  The  un- 


COPPER.  285 

altered  ferrous  sulphide  remaining  in  the  roasted  mass  then 
reacts  with  the  cupric  oxide  formed,  and  the  result  is  cuprous 
sulphide  and  ferrous  oxide.  The  latter  unites  with  the  silica, 
forming  ferrous  silicate,  which  is  very  fusible,  and  is  drawn  off 
as  slag,  while  cuprous  sulphide  containing  some  iron  sulphide 
collects  on  the  hearth  of  the  furnace.  This  product,  which  is 
called  copper  matte,  is  broken  up,  and  repeatedly  roasted  until 
nearly  all  the  sulphur  is  expelled,  and  a  considerable  propor- 
tion of  the  copper  is  reduced  to  the  metallic  state ;  the  more 
oxidizable  foreign  metals  present  become  oxidized,  and,  on  the 
addition  of  silicious  matters,  are  converted  into  fusible  silicates 
by  an  increased  temperature.  The  black  copper  so  obtained 
contains  from  90  to  94  per  cent,  of  copper,  the  remainder  being 
lead,  iron,  sulphur,  arsenic,  etc. 

The  extraction  of  copper  from  the  matte  is  now  frequently  effected  by 
forcing  air  through  the  molten  material  in  a  Bessemer  converter  (p.  312). 
The  iron  and  part  of  the  copper  are  oxidized,  while  sulphur  dioxide  is  dis- 
engaged. The  remaining  sulphide  of  copper  then  reacts  with  the  cuprous 
oxide  so  as  to  yield  the  metal,  and  the  ferrous  oxide  forms  a  slag  with  the 
silicious  lining  of  the  converter. 

The  crude  metal  may  be  refined  by  melting  it  on  the  hearth 
of  a  reverberatory  furnace  and  exposing  it  to  an  oxidizing 
atmosphere.  The  impurities  are  thus  completely  oxidized  and 
removed,  either  by  volatilizing  or  by  forming  a  slag.  After 
removing  the  latter,  some  of  the  copper  is  allowed  to  oxidize 
to  destroy  the  last  traces  of  sulphur.  The  cuprous  oxide  is 
finally  reduced  by  stirring  the  molten  metal  with  poles  of  green 
wood ;  the  combustible  gases  formed  by  the  action  of  the  high 
temperature  on  the  wood  completely  deoxidize  the  copper,  and 
the  cold  metal  is  red  and  soft. 

Another  mode  of  refining,  known  as  the  electrolytic  process, 
consists  in  dissolving  the  impure  copper  in  an  acid,  and  then 
precipitating  the  metal  by  means  of  the  electric  current.  In  an 
acid  bath  of  copper  sulphate  solution,  plates  of  the  crude  metal, 
constituting  the  anodes,  alternate  with  thin  copper  plates  which 
serve  as  cathodes.  The  current  causes  the  anodes  to  dissolve, 


286  LESSONS    IN    CHEMISTRY. 

while  it  deposits  an  equal  amount  of  copper  upon  the  cathodes : 
some  of  the  impurities,  including  the  silver  and  gold,  remain 
undissolved,  forming  the  valuable  anode  mud ;  the  others  are 
retained  in  the  bath.  A  very  pure  product  is  thus  obtained. 

In  the  Lake  Superior  district,  where  enormous  quantities  of 
native  copper  are  found,  the  metal  is  separated  from  the  rock 
by  mechanical  means,  and  subsequently  subjected  to  a  refining 
process  analogous  to  that  first  described.  "  Lake  Copper"  in*, 
eludes  the  most  valued  brands  of  the  copper  of  commerce :  it 
is  remarkable  for  its  high  electric  conductivity. 

Large  quantities  of  copper  are  extracted  also  by  the  wet 
process,  particularly  from  the  burnt  pyrites  of  the  sulphuric 
acid  works.  In  furnaces  of  peculiar  construction  the  ore  mixed 
with  common  salt  is  roasted,  whereby  the  copper  is  converted 
into  cupric  chloride.  This  is  extracted  with  water,  and  the 
copper  then  precipitated  in  the  metallic  state  by  placing  scrap- 
iron  in  the  solution. 

CuCl2         +         Pe         =         FeCl2         +         Cu 

Cement  copper  is  obtained  by  precipitating  with  iron  the  cop- 
per sulphate  solutions  occurring  in  certain  localities. 

Copper  has  a  red  color  and  a  brilliant  lustre.  Its  density  is 
about  8.9.  It  is  exceedingly  ductile,  malleable,  and  tenacious, 
and  one  of  the  best  conductors  of  heat  and  electricity.  It 
melts  at  about  1100°,  and  may  be  crystallized  either  by  fusion 
or  by  electrolysis  of  solutions  of  its  salts.  It  vaporizes  in  the 
electric  arc,  and  in  the  oxyhydrogen  flame. 

Copper  is  unaltered  by  cold  dry  air.  but  by  moist  air  it  is 
gradually  converted  into  a  hydrocarbonate,  which  appears  in  green 
spots  on  the  surface  of  the  metal.  This  is  the  substance  ordinarily 
called  verdigris  (see  §  333). 

At  a  temperature  about  redness,  copper  combines  directly  with 
oxygen,  forming  either  cupric  oxide,  CuO,  or  cuprous  oxide, 
Cu20,  according  to  the  access  of  air.  When  copper  acetate  is 
strongly  heated  in  a  hard  glass  tube,  it  is  entirely  decomposed, 
and  a  residue  of  finely-divided  copper  is  obtained.  If  this  be 
turned  out  and  heated  at  one  point  by  a  lighted  match,  a  black 


COPPER.  287 

spot  appears  and  rapidly  spreads  over  the  entire  mass,  which  is  so 
converted  into  cupric  oxide. 

We  have  already  studied  the  action  of  sulphuric  and  nitric 
acids  on  copper.  Hydrochloric  acid  attacks  it  only  when  boiling, 
and  then  but  slowly,  evolving  hydrogen,  and  forming  cuprous 
chloride,  Cu2CP. 

Ammonia  in  presence  of  oxygen  exerts  a  curious  action  on  copper.  We  in- 
troduce some  copper  clippings  and  a  little  ammonia  into  a  bottle,  which  we 
tightly  cork  and  then  agitate  for  a  few  minutes.  The  liquid  becomes  blue, 
and  if  we  invert  the  bottle  and  open  it  with  its  mouth  under  water,  the  latter 
will  rise  in  the  bottle,  showing  that  part  of  the  air  has  been  absorbed.  It  is 
the  oxygen  which  is  absorbed,  and  the  blue  liquid  contains  copper  nitrite  and 
ammoniacal  cupric  oxide,  both  of  which  are  soluble  in  ammonia.  This  liquid 
is  capable  of  dissolving  cotton,  linen,  paper,  and  other  forms  of  cellulose. 

Copper  is  used  for  the  manufacture  of  boilers,  stills,  con- 
densing apparatus,  and  other  utensils  for  the  laboratory,  manu- 
factory, and  kitchen.  As  wire,  it  is  extensively  used  for  electrical 
purposes.  In  sheets,  it  serves  for  sheathing  ships,  and  some- 
times for  roofing.  It  constitutes  part  of  many  alloys,  among 
which  are  brass,  containing  from  65  to  90  per  cent,  copper,  the 
remainder  being  zinc ;  a  large  proportion  of  copper  gives  a  red 
color  to  the  brass ;  these  metals  are  melted  together  in  crucibles, 
the  zinc  being  added  after  the  copper  is  fused.  Bronze  contains 
from  93  to  95  per  cent,  of  copper,  the  remainder  being  tin,  with 
sometimes  1  per  cent,  of  zinc.  Gun -metal  is  about  91  per  cent, 
copper  and  9  per  cent.  tin.  Bell-metal  and  the  very  white  specu- 
lum metal  contain  respectively  78  and  67  per  cent,  of  copper,  the 
remainder  being  tin.  German  silver  is  an  alloy  of  copper,  zinc, 
and  nickel.  The  United  States  cents  contain  95  per  cent,  of 
copper,  2.5  per  cent,  of  zinc,  and  2.5  per  cent,  of  tin. 

479.  Copper  forms  two  series  of  compounds.     It  is  a  diatomic 
element,  and  in  the  cuprous  compounds  two  atoms  of  copper  form 
a  diatomic  couple,  Cu-Cu,  which  replaces  two  atoms  of  hydrogen 
in  the  acids.     In  the  cupric  compounds,  a  single  diatomic  atom 
of  copper  replaces  two  atoms  of  hydrogen. 

480.  CUPROUS  CHLORIDE,  Cu2CP,  may  be  made  by  boiling  a 
solution  of  cupric  chloride  with  copper,  or  by  boiling  copper  with 
hydrochloric  acid  and  adding  a  little  nitric  acid  from  time  to  time ; 


288  LESSONS    IN    CHEMISTRY. 

in  the  latter  case,  cupric  chloride  is  formed,  and  is  at  once  re- 
duced by  the  metallic  copper  present.  On  adding  water  to  the 
brown  liquid  so  obtained,  cuprous  chloride  is  thrown  down  as  a 
white  crystalline  precipitate.  It  is  insoluble  in  water,  but  dis- 
solves in  ammonia,  forming  a  colorless  solution  which  absorbs 
oxygen  and  becomes  blue  on  exposure  to  air.  It  also  dissolves 
in  hydrochloric  acid,  and  both  of  these  solutions  are  capable  of 
absorbing  a  large  volume  of  carbon  monoxide. 

481.  CUPRIC  CHLORIDE,  CuCP,  is  obtained  when  cupric  oxide 
is  boiled  in  hydrochloric  acid.    When  the  green  solution  is  suf- 
ficiently concentrated,  it  deposits  beautiful  bluish-green  crystals 
of  cupric  chloride,  with  two  molecules  of  water  of  crystallization. 

A  hydrated  compound  of  cupric  chloride  and  cupric  oxide 
is  met  with  in  the  beautiful  green  mineral  atacamite. 

482.  CUPROUS  OXIDE,  Cu20. — This  substance  constitutes  the 
beautiful  mineral  cuprite  which  occurs  in  red  octahedra  and 
cubes.     It  may  be  made  by  boiling  glucose  with  a  solution  of 
cupric  acetate,  and  is  then  thrown  down  as  a  bright  red  crys- 
talline precipitate.     If  heated  in  contact  with  air,  it  is  con- 
verted into  cupric  oxide.     The  color  of  red  copper  glass  is  due 
to  the  presence  of  this  compound. 

483.  CUPRIC  OXIDE,  CuO. — When  cupric  nitrate  is  strongly 
heated,  it  yields  a  fine  black  powder  of  cupric  oxide.     This  com- 
pound is  usually  prepared  by  heating  metallic  copper  to  redness  in 
vessels  through  which  air  is  blown  or  drawn.     The  copper  then 
absorbs  oxygen,  and  is  converted  into  hard  and  compact  cupric 
oxide.     This  substance  is  reduced  by  both  hydrogen  and  charcoal 
at   temperatures   below  redness,  water   or  carbon  dioxide  being 
formed.     It  communicates  a  green  color  to  glass,  and  is  used  for 
that  purpose.     In  the  laboratory  it  is  of  great  value  in  the  analysis 
of  carbon  compounds. 

When  potassium  or  sodium  hydroxide  is  added  to  the  solution  of 
a  cupric  salt,  cupric  hydroxide,  Cu(OH)2,  is  formed  as  a  pale-blue 
precipitate.  When  the  liquid  containing  this  hydroxide  is  boiled, 
the  precipitate  turns  black,  for  it  is  converted  into  cupric  oxide 
and  water,  even  when  surrounded  by  liquid. 


COMPOUNDS    OF    COPPER.  289 

484.  CUPROUS  SULPHIDE,  Cu2S. — This  is  the  mineral  chalco- 
cite.      It  may  be  obtained  as  a  black,  brittle,  crystalline  mass  by 
fusing  together  sulphur  and  copper,  or  by  burning  copper  in  vapor 
of  sulphur. 

485.  CUPRIC  SULPHIDE,  CuS,  is  thrown  down  as  a  brownish- 
black  precipitate  by  the  action  of  hydrogen  sulphide  on  cupric 
solutions.     When  heated,  it  loses  sulphur,  and  is  converted  into 
cuprous  sulphide. 

486.  CARBONATES  OP  COPPER. — When  a  solution  of  cupric 
sulphate  is  treated  with  sodium  carbonate,  carbon  dioxide  is  dis- 
engaged, and   a  bluish-green  precipitate  is   thrown  down  ;  when 
washed  with  warm  water,  its  color  becomes  green ;  it  is  a  com- 
pound   of    cupric    hydroxide    and    cupric    carbonate,   containing 
CuC03.Cu(OH)J.     The  beautiful  green  mineral  malachite,  which 
when  polished  displays  veins  of  variegated  tints,  is  a  compound 
having  the  same  composition.     Azurite,  a  mineral  found  in  fine 
blue  crystals,  is  a  compound  of  two  molecules  of  cupric  carbonate 
with  one  of  cupric  hydroxide,  Cu(OH)2.2CuC03. 

487.  TESTS  FOR  COPPER. — The  salts  of  copper  have  either  blue 
or  green  colors.     Both  hydrogen  sulphide  and  ammonium  sulphide 
throw  down  brownish-black  precipitates.     The  alkaline  hydroxides 
precipitate  pale-blue  cupric  hydroxide,  insoluble  in  an  excess  of  the 
reagent.      Ammonia   also   produces  a  pale-blue  precipitate,  but 
this  dissolves  when  an  excess  of  ammonia  is   added,  yielding  a 
magnificent  blue  solution  of  an  ammonio-cupric  salt. 

Potassium  ferrocyanide  produces  a  mahogany-brown  precipitate 
of  cupric  ferrocyanide,  and  the  test  is  exceedingly  delicate  and 
characteristic.  A  clean  piece  of  iron,  as  a  needle  or  knife-blade, 
dipped  in  a  cupric  solution,  quickly  becomes  covered  with  a  red 
layer  of  metallic  copper :  this  test  is  conclusive. 


19 


290 


LESSONS    IN    CHEMISTRY. 


LESSON    LV. 


MERCURY.     Hg  =  200. 

488.  Mercury  is  found  in  small  quantity  in  the  metallic  state, 
but  its  principal  ore  is  the  sulphide,  which  constitutes  the  mineral 
cinnabar.  It  is  especially  abundant  in  Spain  and  on  the  Pacific 
slope. 

The  reduction  of  cinnabar  is  a  simple  operation :  it  is  broken 
up  and  roasted  in  a  current  of  air,  the  sulphur  being  expelled  as 
sulphur  dioxide,  while  mercury  distils.  Very  little  improvement 
has  been  effected  in  the  furnaces  during  hundreds  of  years ;  the 
mercury  vapor  is  sometimes  condensed  by  being  passed  through  a 
long  series  of  clay  pipes,  sometimes  by  being  directed  through  a 
number  of  chambers  containing  a  layer  of  water,  by  which  the 
are  cooled  (Fig.  117).  The  mercury  is  then  filtered  through 


FIG.  117. 


closely-woven  canvas,  and  is  usually  transported  in  iron  bottles, 
each  bottle  holding  about  sixty  pounds. 

Mercury  is  liquid  at  ordinary  temperatures  :  it  freezes  at  —  40°, 
and  boils  at  357°.     Its  density  at  0°  is  about  13.6. 


MERCURY.  291 

The  density  of  mercury  vapor  compared  with  that  of  hydrogen  is  100  :  its 
atomic  weight  is  200,  as  is  shown  by  the  vapor-densities  of  its  volatile  com- 
pounds. Then  if  equal  volumes  of  gases  contain  equal  numbers  of  molecules, 
and  if  the  molecule  of  hydrogen  contain  two  atoms,  the  molecule  of  mercury 
vapor  must  consist  of  a  single  atom.  This  is  the  case  also  with  zinc,  cadmium, 
argon,  helium,  and  a  few  other  elements. 

Mercury  is  unaffected  by  the  air  at  ordinary  temperatures,  but 
at  300°  it  absorbs  oxygen  and  is  converted  into  red  mercuric 
oxide.  It  combines  directly,  and  in  the  cold,  with  chlorine,  bro- 
mine, and  iodine,  and  with  sulphur  by  the  aid  of  a  gentle  heat,  or 
if  the  sulphur  be  finely  divided.  Mercury  is  not  dissolved  by 
hydrochloric  acid  :  boiling  sulphuric  acid  converts  it  into  mercuric 
sulphate,  sulphur  dioxide  being  disengaged.  Nitric  acid  dissolves 
it,  emitting  red  vapors,  and  forming  mercurous  nitrate  if  the  re- 
action take  place  in  the  cold,  or  mercuric  nitrate  if  the  acid  be 
boiling. 

Mercury  is  used  for  filling  thermometers,  barometers,  and  press- 
ure-gauges ;  for  silvering  ordinary  mirrors,  which  are  coated  with 
tin  foil  amalgamated  with  mercury ;  for  the  extraction  of  silver 
and  gold  from  their  ores;  and  for  the  preparation  of  various 
amalgams. 

The  mercury  of  commerce  is  rarely  pure ;  it  contains  small 
quantities  of  lead,  copper,  tin,  and  sometimes  bismuth.  Its  ap- 
proximate purity  may  be  determined  by  allowing  a  few  drops  to 
fall  on  a  clean  piece  of  paper  or  porcelain  ;  pure  mercury  will 
then  break  up  into  small  globules  which  are  perfectly  round,  and 
move  about  freely  when  the  surface  on  which  they  rest  is  inclined, 
but  mercury  containing  other  metals  forms  globules  that  are  drawn 
out  to  a  tail,  and  that  do  not  move  so  readily.  The  surface  of 
pure  mercury  is  perfectly  brilliant,  but  when  impure  the  metal 
has  a  tarnished  appearance.  It  may  be  purified  by  treating  the 
metal  in  a  finely  divided  state  with  very  dilute  nitric  acid,  or 
by  distillation  in  vacuo. 

Like  copper,  mercury  is  diatomic,  and  forms  two  series  of  com- 
pounds,— mercurous  compounds,  in  which  two  atoms  form  a  di- 
atomic couple,  and  mercuric  compounds,  in  which  two  atoms  of 
hydrogen  are  replaced  by  a  single  diatomic  mercury  atom. 


292  LESSONS    IN    CHEMISTRY. 

489.  MERCUROUS  CHLORIDE,  Hg2Cl2. — This  compound  is  the 
well-known  medicine  calomel.    It  is  made  by  subliming  a  mixture 
of  mercurous  sulphate  and  common  salt. 

Hg'SO4          +          2NaCl        =         Na2SO*          +          Hg2Cl2 
Mercurous  sulphate.  Mercurous  chloride. 

The  calomel  then  condenses  in  appropriate  receivers,  in  dense 
crystalline  masses.  It  is  usually  resublimed,  and  its  vapors  passed 
into  jars  or  chambers  filled  with  steam,  where  it  condenses  in  an 
impalpable  powder.  Calomel  is  precipitated  when  hydrochloric 
acid  is  added  to  the  solution  of  a  mercurous  salt. 

In  masses,  calomel  occurs  in  dense,  fibrous,  crystalline,  and 
translucent  fragments,  colorless  when  recently  prepared,  but  be- 
coming gray  or  yellowish  by  the  action  of  light  which  partially 
decomposes  this  compound  into  mercuric  chloride  and  mercury. 
Its  density  is  about  7.2.  It  is  insoluble  in  water ;  when  calomel 
is  agitated  with  water  and  the  liquid  filtered,  no  turbidity  should 
be  produced  in  the  filtrate  by  the  addition  of  sodium  carbonate 
solution.  If  mercurous  chloride  be  heated  with  a  solution  of 
sodium  chloride,  it  is  converted  into  mercuric  chloride,  while 
metallic  mercury  is  deposited  as  a  gray  powder. 

490.  MERCURIC  CHLORIDE,  HgCl2,  is  the  poisonous  compound 
corrosive  sublimate.      It  is  prepared  by  subliming  a  mixture  of 
common  salt  and  mercuric  sulphate,  sodium  sulphate  being  formed 
at  the  same  time. 

HgSO*        +        2NaCl        =        Na'SO*         +         HgCP 
Mercuric  sulphate.  Mercuric  chloride. 

It  is  also  formed  by  the  direct  combination  of  chlorine  and 
mercury. 

It  forms  dense,  white  or  colorless,  crystalline  masses,  having  a 
density  of  6.5.  It  melts  at  265°,  and  boils  at  about  295°.  It  is 
soluble  in  nineteen  times  its  weight  of  cold  water,  and  in  much 
less  boiling  water,  from  which  it  separates  in  anhydrous  crystals 
on  cooling.  It  is  exceedingly  poisonous,  and  its  antidote  is  white 
of  egg,  for  it  forms  an  insoluble  compound  with  albumen. 

491.  MERCUROUS  IODIDE,  Hg2!2,  is  obtained  as  a  green  powder 
by  rubbing  together  in  a  mortar  100  parts  of  mercury  and  63.5 


COMPOUNDS  OF  MERCURY.  293 

parts  of  iodine  with  a  few  drops  of  alcohol.  By  the  action  of 
light  or  heat,  it  is  decomposed  into  mercuric  iodide  and  metallic 
mercury. 

492.  MERCURIC  IODIDE,  HgP. — This  beautiful  compound  is 
prepared  by  mixing  potassium  iodide  with  four-fifths  its  weight 
of  mercuric  chloride,  both  in  aqueous  solution,  and  thoroughly 
washing  the  precipitate. 

HgCl2     +     2KI     =     HgP     +     2KC1 

If  either  substance  be  employed  in  excess,  the  precipitate  will  be 
redissolved. 

So  obtained,  mercuric  iodide  forms  a  dark-red  powder,  which  is 
almost  insoluble  in  water,  but  dissolves  slightly  in  boiling  alcohol, 
and  on  cooling  separates  in  red,  octahedral  crystals. 

Mercuric  iodide  presents  a  curious  case  of  dimorphism.  If  a 
little  of  the  red  powder  be  cautiously  heated  on  a  sheet  of  white 
paper  on  which  it  is  spread  out,  the  red  color  changes  to  yellow ; 
the  yellow  particles  are  rhombic  prisms,  and  if  they  be  rubbed 
with  a  glass  rod  or  any  hard  body,  they  will  reassume  the  red  color 
and  their  first  crystalline  form,  the  octahedron.  Mercuric  iodide 
melts  to  a  dark-yellow  liquid,  and  volatilizes,  condensing  in  the 
yellow  crystals. 

With  potassium  iodide,  mercuric  iodide  forms  a  soluble  com- 
pound, which  may  be  obtained  by  dissolving  the  mercuric  iodide 
in  solution  of  potassium  iodide.  The  colorless  liquid,  made 
strongly  alkaline  with  caustic  potash,  constitutes  JVessfer's  reagent, 
which  is  used  in  the  laboratory  as  a  test  for  ammonia  and  com- 
pound ammonias,  with  which  it  forms  a  brownish  cloud  or  a  dense 
precipitate,  according  to  the  proportion  of  ammonia  present. 

493.  MERCUROUS  OXIDE,  Hg20. — This  substance  is  obtained 
as  a  black  powder  by  digesting  mercurous  chloride  in  a  solution 
of  potassium  hydroxide.     A  temperature  of  100°,  or  the  prolonged 
action  of  light,  decomposes  it  into  mercuric  oxide  and  mercury. 

494.  MERCURIC  OXIDE,  HgO,  has  long  been  known  under  the 
name  red  precipitate.     It  may  be  made  either  by  decomposing 
mercuric  nitrate  by  heat  until  the  whole  is  converted  into  a  red 
powder  and  no  more  red  vapors  are  disengaged,  or  by  adding  po- 


294  LESSONS   IN   CHEMISTRY. 

tassium  hydroxide  to  a  solution  of  mercuric  chloride  and  thoroughly 
washing  the  precipitate.  Prepared  in  the  first  manner,  it  forms 
a  red,  crystalline  powder ;  obtained  by  precipitation,  it  is  yellow 
and  amorphous,  but  becomes  red  when  heated. 

Mercuric  oxide  is  insoluble  in  water :  when  it  is  heated,  its  color 
darkens,  and  at  a  temperature  of  about  400°  it  is  decomposed  into 
metallic  mercury  and  oxygen.  It  is  an  energetic  oxidizing  agent. 
In  presence  of  water,  it  converts  chlorine  into  hypochlorous  acid, 
and  when  dry  and  quite  cold,  into  hypochlorous  oxide.  If  a  mix- 
ture of  a  little  mercuric  oxide  and  sulphur  be  heated  in  a  test-tube, 
it  explodes. 

495.  MERCURIC  SULPHIDE,  HgS. — This  is  the  mineral  cin- 
nabar, which  is  found  in  hard  dense  masses,  and  in  transparent 
red  crystals.    It  is  manufactured  by  grinding  together  the  required 
proportions  of  mercury  and  sulphur,  and  subliming  the  resulting 
black  mass.     It  then  forms  a  dark-red,  crystalline  solid,  having  a 
density  of  8.12.     When  strongly  heated  out  of  contact  with  air, 
it  volatilizes  without  melting.     When  heated  in  the  air,  it  takes 
fire,  and  burns  with  a  blue  flame,  mercury  vapor  and  sulphur 
dioxide  being  disengaged. 

The  fine  scarlet  pigment  vermilion  is  very  finely  divided  mer- 
curic sulphide,  made  by  grinding  for  a  long  time  in  a  mortar  a 
mixture  of  300  parts  of  mercury  and  114  parts  of  flowers  of 
sulphur :  75  parts  of  potassium  hydroxide  dissolved  in  400  parts 
of  water,  are  then  added,  and  the  grinding  is  continued,  the  mortar 
being  kept  at  a  temperature  of  about  45°.  When  the  powder  has 
assumed  the  desired  shade,  it  is  quickly  washed  with  hot  water, 
and  dried. 

496.  TESTS  FOR  MERCURY. — Very  few  of  the  mercurous  salts 
are  soluble :  in  their  solutions,  hydrochloric  acid  produces  a  white 
precipitate  of  mercurous  chloride ;  hydrogen  sulphide  and  potassium 
and  sodium  hydroxides  and  ammonia  produce  black  precipitates. 

With  mercuric  salts,  hydrogen  sulphide  and  ammonium  sulphide 
give  black  precipitates;  potassium  hydrate  throws  down  yellow 
mercuric  oxide.  If  a  piece  of  bright  copper  be  dipped  into  the 
slightly  acid  solution  of  either  a  mercurous  or  a  mercuric  salt, 


BISMUTH.  295 

metallic  mercury  is  quickly  deposited  on  the  copper,  whose  surface 
becomes  white  and  brilliant  after  a  little  friction. 

When  heated  with  lime  or  sodium  carbonate  in  a  small  glass 
tube,  all  compounds  of  mercury  yield  a  sublimate  of  metallic  mer- 
cury, which  condenses  in  the  cooler  part  of  the  tube  in  microscopic 
globules.  On  throwing  a  fragment  of  iodine  into  the  still  warm 
tube,  the  globules  are  changed  into  yellow  or  red  mercuric  iodide. 


LESSON    LVI. 
BISMUTH  AND   GOLD. 

These  two  metals  are  triatomic  :  they  form  chlorides  whose  molecules  contain 
one  atom  of  metal  and  three  atoms  of  chlorine.  They  form  trioxides,  containing 
two  atoms  of  metal  and  three  of  oxygen.  Of  bismuth  we  know  also  a  dioxide, 
Bi202,  a  tetroxide,  Bi2O,  and  a  pentoxide,  Bi205,  and  gold  forms  an  oxide, 


497.  Bismuth,  Bi  =  206.5.  —  Bismuth  is  found  in  the  metallic 
state  disseminated  in  quartz.  It  is  separated  from  the  earthy 
materials,  which  are  called  the  gangue,  by  heating  the  mineral  in 
iron  tubes  which  are  closed  at  one  end,  and  arranged  in  an  in- 
clined position  in  a  furnace  beyond  which  the  lower  and  open  end 
projects.  The  bismuth  then  melts  and  runs  out  of  the  tubes. 
The  bismuth  thus  obtained  is  never  pure,  but  contains  small 
quantities  of  other  metals,  and  sometimes  traces  of  arsenic  and 
sulphur.  In  order  to  purify  it,  it  is  pulverized  and  mixed  with  a 
little  potassium  nitrate  :  the  mixture  is  heated  to  redness  in  clay 
crucibles;  the  impurities,  which  are  more  easily  oxidized  than 
the  bismuth,  are  thus  oxidized,  and  any  arsenic  present  is  con- 
verted into  potassium  arsenate. 

Bismuth  is  a  crystalline,  brittle,  reddish-white  metal.  Its 
density  is  9.8.  It  melts  at  264°.  By  allowing  a  crucible  full  of 
the  molten  metal  to  cool  until  a  crust  forms  on  the  surface,  and 
then  pouring  out  the  liquid  interior  through  a  hole  made  in  the 
crust,  fine  crystals  of  bismuth  may  be  obtained.  These  crystals 
become  superficially  oxidized,  and  the  thin  film  of  oxide  imparts 


296  LESSONS   IN   CHEMISTRY. 

to  them  all  the  colors  of  the  rainbow.  Bismuth  is  unaffected  by 
cold  air,  but  at  a  red  heat  it  is  burned  to  bismutb  oxide.  It  dis- 
solves in  nitric  acid,  forming  bismuth  nitrate,  while  red  vapors  are 
disengaged. 

In  addition  to  its  use  for  the  preparation  of  the  bismuth  com- 
pounds, this  metal  is  employed  chiefly  for  the  manufacture  of 
certain  alloys.  Britannia  metal  contains  about  one  per  cent,  of 
bismuth.  The  fusing  points  of  the  bismuth  alloys  are  much 
lower  than  that  of  bismuth.  A  mixture  known  as  Wood's  alloy 
or  fusible  metal  consists  of  one  or  two  parts  of  cadmium,  two 
parts  of  tin,  four  of  lead,  and  seven  or  eight  of  bismuth.  It 
melts  between  66°  and  71°,  according  to  its  composition.  An- 
other alloy,  known  as  Arcet's  fusible  metal,  is  made  by  melting 
together  eight  parts  of  bismuth,  five  of  lead,  and  three  of  tin. 
It  melts  at  94.5°. 

Bismuth  much  resembles  antimony  in  many  of  its  chemical  re- 
lations ;  but  we  class  it  among  the  metals,  because  it  is  capable  of 
replacing  the  hydrogen  of  oxygen  acids,  so  forming  well-defined 
salts. 

498.  BISMUTH   CHLORIDE,  Bid3. — This  compound  results  from  the  direct 
union  of  chlorine  and  bismuth.     When  powdered  bismuth  is  sprinkled  into 
chlorine,  it  burns  brilliantly,  forming  the  chloride.     This  substance  is  pre- 
pared by  passing  dry  chlorine  over  melted  bismuth  in  a  retort  so  arranged 
that  the  chloride  may  collect  in  a  receiver  as  it  distils.     It  then  forms  a  crys- 
talline deliquescent  mass,  which  is  quite  soft  at  ordinary  temperatures,  being 
very  fusible.    It  is  soluble  in  hydrochloric  water,  but  is  decomposed  by  water, 
hydrochloric  acid  being  formed,  while  a  white  powder  of  bismuth  oxychloride, 
BiOCl,  is  thrown  down. 

2BiCl3         +         2H2Q        =         4HC1         +         2BiOCl 

Bismuth  oxychloride  constitutes  the  cosmetic  known  as  pearl-white. 

499.  BISMUTH  OXIDE,  Bi203,  is  obtained  as  a  yellow  powder  when  bismuth 
nitrate  is  strongly  heated.     It  melts  at  a  red  heat,  and  on  cooling  solidifies  to 
a  glassy,  yellow  mass.     It  forms  a  very  fusible  silicate,  and  therefore  cannot 
be  melted  in  clay  crucibles.     Bismuth  hydroxide,  probably  Bi(OH)3,  is  thrown 
down  as  a  white  powder  when  bismuth  subnitrate  is  treated  with  potassium 
hydroxide  or  ammonia-water. 

500.  BISMUTH  NITRATE,  Bi(N03)3. — When  bismuth  is  boiled 
with  nitric  acid,  and  the  solution  is  concentrated,  large,  colorless, 


GOLD.  297 

deliquescent  crystals  of  bismuth  nitrate  with  three  molecules  of 
water  of  crystallization  are  deposited.  Since  bismuth  is  triatomic, 
one  atom  of  bismuth  will  replace  the  hydrogen  in  three  molecules 
of  nitric  acid,  and  combine  with  the  three  groups  NO3.  The 
crystals  of  bismuth  nitrate  are  very  soluble  in  water  containing 
free  nitric  acid ;  but  if  the  solution  be  diluted  with  a  large  volume 
of  water,  a  pulverulent  white  precipitate  is  thrown  down.  This 
contains  (BiO)NO3,  or  BiNO4,  and  is  employed  in  medicine  under 
the  name  subnitrate  of  bismuth.  A  larger  quantity  may  be  ob- 
tained by  adding  very  dilute  ammonia  to  the  liquid. 

501.  TESTS  FOR  BISMUTH. — When  solutions  of  the  bismuth 
salts  are  largely  diluted  with  water,  white  precipitates  of  sub-salts 
are  thrown  down.     Hydrogen  sulphide  and  ammonium  sulphide 
occasion  brown  precipitates  of  bismuth  sulphide.     The  alkaline 
carbonates  and  hydroxides  yield  white  precipitates,  insoluble  in  an 
excess  of  the  reagent. 

When  a  bismuth  salt  is  heated  with  sodium  carbonate  in  the 
inner  flame  of  a  blow-pipe,  a  brittle  bead  of  metallic  bismuth  is 
obtained. 

502.  Gold,  Au  —  195.7.— Gold  is  found  in  the  metallic  state, 
sometimes  in  masses  called  nuggets,  but  more  usually  in  small 
particles  disseminated  through  quartz  rock,  or  the  sand  produced 
by  the  disintegration  of  the  rock.    It  is  sometimes  associated  with 
silver,  copper,  lead,  and  tellurium.     The  gold  is  extracted  from 
gold-bearing  sand  by  washing  the  latter  in  a  stream  of  running 
water  in  troughs  called  cradles.     By  reason  of  its  great  density, 
the  gold  then  sinks  to  the  bottom,  while  the  lighter  sand  is  carried 
on  with  the  water.     The  gold  may  then  sometimes  be  removed  at 
once;  sometimes  it  is  in  such  small  particles  that  it  must  be  amal- 
gamated with  mercury,  as  will  presently  be  described.     Quartz 
rock  containing  gold  is  crushed  by  powerful  machinery,  and  the 
greater  part  of  the  earthy  matter  is  removed  by  washing  in  vessels 
containing  mercury,  which  forms  an  amalgam  with  the  gold.    Fig. 
118   represents  an  apparatus  which  is  sometimes  employed  for 
grinding  together  the  mercury  and  crushed  rock.     It  consists  of 
inclined  iron  basins,  each  containing  two  cast-iron  balls :  the  rock 


298  LESSONS    IN    CHEMISTRY 

and  mercury  being  introduced  into  these  vessels,  a  motion  of  rota- 
tion is  communicated  by  machinery,  and  by  the  friction  of  the 


FIG.  11?. 

balls  the  rock  is  reduced  to  an  impalpable  powder,  which  is  carried 
off  by  a  current  of  water  flowing  through  the  basins,  while  the 
gold  amalgamates  with  the  mercury.  From  the  resulting  amal- 
gam the  mercury  is  removed  by  distillation. 

Very  large  quantities  of  gold  are  now  obtained  by  what  is 
known  as  the  cyanide  process.     It  depends  upon  the  solubility 
of  metallic  gold  in  a  solution  of  potassium  cyanide  (see  p.  168). 
Au     +     2KCN     +     H20     =     KAu(CN)2     +     KOH     +     H 

When  the  crushed  rock  containing  gold  in  a  finely  divided 
state  is  treated  with   dilute  potassium   cyanide  solution,   the 
greater  part  of  the  metal  is  dissolved.     It  may  be  precipitated 
by  the  electric  current  or  by  means  of  metallic  zinc. 
2KAu(CN)2     +     Zn     =     R2Zn(CN)*     +     2Au 

As  extracted  from  its  native  rocks  or  sand,  gold  is  rarely  pure. 
It  usually  contains  more  or  less  silver ;  this  may  be  removed  by 
boiling  the  metal  in  nitric  acid,  which  does  not  affect  the  gold, 
while  it  converts  the  silver  into  silver  nitrate.  However,  if  only 
a  small  proportion  of  silver  be  present,  that  metal  is  protected 
by  the  gold,  and  it  is  necessary  to  melt  the  alloy  with  a  larger 
proportion  of  silver  before  boiling  it  with  nitric  acid.  The  gold 
then  remains  as  a  spongy  mass.  Pure  gold  may  also  be  obtained 
by  adding  ferrous  sulphate  or  oxalic  acid  to  a  solution  of  gold 


AURIC    CHLORIDE.  299 

chloride ;  in  this  case  the  gold  is  thrown  down  as  a  dark-brown, 
dull  powder,  capable  of  assuming  its  natural  high  lustre  by 
burnishing. 

The  color  of  gold  varies  from  greenish  yellow  to  a  red  almost 
as  decided  as  that  of  copper.  Light  which  has  been  successively 
reflected  from  ten  surfaces  of  gold  is  scarlet.  Gold  is  quite  soft, 
and  the  most  malleable  and  ductile  of  the  metals.  Its  density  is 
19.3 ;  it  melts  at  about  1200°,  and  at  a  higher  temperature  emits 
a  green  vapor.  A  thin  gold-leaf,  carefully  spread  out  between 
two  plates  of  glass,  allows  the  passage  of  a  faint  green  light. 

Gold  is  not  oxidized  by  air,  either  moist  or  dry,  or  at  any  tem- 
perature. It  is  not  affected  by  boiling  with  nitric,  sulphuric,  or 
hydrochloric  acids.  Nitro-hydrochloric  acid  dissolves  it,  disen- 
gaging red  vapors,  and  forming  a  yellow  solution  of  gold  tri- 
chloride ;  the  nitro-hydrochloric  acid  employed  for  dissolving  gold 
is  a  mixture  of  nitric  acid  with  four  times  its  weight  of  hydro- 
chloric acid.  Gold  is  also  attacked  by  selenic  acid,  H2Se04,  by  a 
hot  mixture  of  iodic  and  sulphuric  acids,  and  by  a  boiling  mixture 
of  concentrated  nitric  and  sulphuric  acids ;  from  the  latter  solu- 
tion the  gold  is  again  deposited  in  the  metallic  state  by  the  addi- 
tion of  water.  Gold  dissolves  readily  in  chlorine-water,  in  bromine, 
and  combines  directly  with  iodine  under  the  influence  of  light. 

Gold  forms  two  series  of  compounds, — aurous  compounds,  in 
which  the  metal  appears  to  be  monatomic,  and  auric  compounds, 
in  which  it  is  triatomic. 

503.  AURIC  CHLORIDE,  AuCl3. — When  the  solution  of  gold  in 
nitro-hydrochloric  acid  is  evaporated,  auric  chloride  is  deposited  as 
a  dark-red  crystalline  mass,  which  is  very  deliquescent.  It  is  very 
soluble  in  water  and  in  ether.  Its  strong  solutions  are  orange 
brown,  but  the  dilute  solution  is  pure  yellow.  It  produces  a  violet 
stain  on  the  skin ;  it  is  decomposed  by  the  action  of  heat,  and 
more  slowly  by  light,  and  is  reduced  by  many  substances,  among 
which  are  phosphorus,  phosphorous  and  sulphurous  acids,  oxalic 
acid,  and  ferrous  sulphate.  A  stick  of  phosphorus  immersed  in 
an  ethereal  solution  of  auric  chloride  becomes  quickly  coated 
with  a  film  of  gold.  The  metal  is  deposited  as  a  brown  powder 


300  LESSONS    IN    CHEMISTRY. 

when  either  ferrous  sulphate  or  oxalic  acid  is  added  to  a  solution 
of  auric  chloride. 

When  a  solution  containing  a  mixture  of  stannous  and  stannic 
chlorides  is  added  to  auric  chloride,  a  flocculent,  purple  precipi- 
tate of  uncertain  composition,  but  containing  gold,  tin,  oxygen,  and 
hydrogen,  is  thrown  down.  This  precipitate  is  known  as  purple 
of  Cassius,  and  is  employed  in  painting  on  glass  and  porcelain. 

When  auric  chloride  is  heated  to  230°,  chlorine  is  disengaged, 
and  an  insoluble  yellow  powder  of  aurous  chloride,  AuCl,  remains. 

There  are  two  oxides  of  gold, — aurous  oxide,  Au20,  and  auric 
oxide,  Au203.  The  first  is  basic,  the  second  forms  aurates  with 
the  metals.  When  caustic  alkalies  are  fused  with  gold  in  contact 
with  air,  alkaline  aurates  are  formed. 

504.  ASSAYING  OF  GOLD. — Gold  coin,  jewelry,  etc.,  are  generally  alloyed 
with  copper,  and  sometimes  with  silver.     A  weighed  quantity  of  the  metal  to 
be  assayed  is  first  melted  with  about  three  times  its  weight  of  silver,  and  the 
resulting  button  is  cupelled  in  a  bone-ash  cupel  ($  433).     The  copper  and  any 
other  base  metals  present  are  so  converted  into  oxides,  which  are  absorbed  by 
the  cupel,  and  a  button  containing  only  gold  and  silver  is  obtained.     This  is 
hammered  out  into  a  thin  sheet,  which  is  twisted  up  and  boiled  in  nitric  acid ; 
the  silver  is  dissolved,  while  the  gold  remains  as  a  spongy  mass,  which  is 
washed,  heated  to  redness,  and  then  weighed. 

The  gold  coin  of  the  United  States  contains  90  per  cent,  of  gold,  the  re- 
mainder being  copper. 

505.  GILDING. — Silver  and  copper  objects  may  be  gilded  by  rubbing  over 
them  an  amalgam  of  gold  with  eight  times  its  weight  of  mercury.     They  are 
then  heated  under  a  chimney  so  arranged  that  the  poisonous  mercury  vapor 
may  be  entirely  carried  off.     The  dull  gilded  surface  is  then  rendered  brilliant 
by  burnishing.     A  thin  film  of  gold  is  deposited  on  copper  objects  when  they 
are  dipped  into  a  hot  solution  of  auric  chloride  with  sodium  carbonate  and 
sodium  phosphate. 

Gilding  is  best  accomplished  by  connecting  the  objects  to  be  gilded  with  the 
zinc  pole  of  a  voltaic  battery,  and  immersing  them  in  a  solution  obtained  by 
boiling  auric  chloride  with  potassium  cyanide.  The  positive  pole  of  the  bat- 
tery is  connected  with  a  plate  of  gold  immersed  in  the  same  liquid. 

The  rare  elements,  gallium,  indium,  and  thallium,  which  were  discovered  by 
the  aid  of  the  spectroscope,  are  related  to  gold  and  bismuth  in  the  general  con- 
stitution of  their  compounds.  Traces  of  indium  and  of  gallium  exist  in  many 
zinc  blendes,  while  small  quantities  of  thallium  occur  in  certain  iron  pyrites, 
and  the  metal  is  obtained  from  the  dust  which  collects  in  the  flues  of  sulphuric 
acid  works  when  these  pyrites  are  burned  for  the  production  of  sulphur  dioxide. 


ALUMINIUM.  301 

LESSON    LVII. 
ALUMINIUM.    Al  =  27. 

506.  This  is  one  of  the  most  abundant  elements,  but  it  is 
found  only  in  combination.  It  may  be  obtained  in  various 
ways,  but  is  now  generally  manufactured  by  decomposing  the 
oxide,  APO3,  dissolved  in  a  bath  of  cryolite,  by  powerful  electrie 
currents.  The  cryolite  is  melted  in  an  electric  furnace  in  which 
the  carbon  lining  forms  the  cathode  and  carbon  rods  the  anode. 
Pure  aluminium  oxide,  or  corundum,  is  now  added :  it  dissolves 
and  is  reduced,  aluminium  collecting  on  the  hearth,  while  the 
oxygen  forms  carbonic  oxide  with  the  positive  carbon.  This 
process  is  continuous. 

Aluminium  was  formerly  obtained  by  heating  a  mixture  of 
the  double  chloride  of  aluminium  and  sodium  with  metallic 

sodium. 

AlCl3,NaCl       +       3Na       =       4NaCl       +       Al 

Aluminium  is  a  tin-white  metal,  capable  of  being  highly 
polished.  It  is  very  ductile  and  malleable,  and  also  very  sonorous. 
It  is  a  good  conductor  of  heat  and  electricity.  Its  density  is  2.56  ; 
it  is  therefore  as  light  as  glass  and  porcelain.  It  melts  at  about 
660°.  It  is  unaltered  by  the  air  at  ordinary  temperatures,  but 
when  melted  absorbs  oxygen  and  is  converted  into  aluminium 
oxide.  It  is  hardly  affected  by  either  nitric  or  sulphuric  acid, 
but  dissolves  readily  in  hydrochloric  acid,  disengaging  hydrogen 
and  forming  aluminium  chloride.  It  is  also  dissolved  by  boiling 
solutions -of  the  alkaline  hydrates,  hydrogen  being  set  free,  while 
alkaline  aluminates  are  formed. 

The  great  tenacity  of  aluminium,  and  its  lightness  and  un- 
changeableness  in  the  air,  render  it  an  exceedingly  valuable 
metal.  It  is  employed  for  scientific  instruments,  cooking  uten- 
sils, ornaments,  and  as  a  reducing  agent  in  certain  metallurgical 
operations. 


302 


LESSONS    IN    CHEMISTRY. 


Aluminium  bronzes  are  alloys  of  copper  and  aluminium.  One 
of  them,  containing  ten  per  cent,  of  aluminium,  possesses  ex- 
traordinary tenacity,  and  does  not  tarnish  in  the  air.  Its  color 
resembles  that  of  gold. 

507.  ALUMINIUM  CHLORIDE,  A1CP. — When  aluminium  or  its 
hydroxide  is  dissolved  in  hydrochloric  acid,  a  solution  of  alu- 
minium chloride  is  obtained,  but  this  solution  cannot  be  evapo- 
rated to  dryness  without  decomposing  into  aluminium  oxide 
and  hydrochloric  acid. 

2A1C13         +        3H20        =         A1203        +        6HC1 

Solid  aluminium  chloride  is  formed  by  passing  chlorine  gas  over 
a  red-hot  mixture  of  aluminium  oxide  and  charcoal,  which  has 
been  made  into  small  balls  with  a  little  oil,  and  then  calcined  in  a 
crucible.  These  balls  are  put  in  a  clay  tube  or  retort,  which  is 
heated  to  bright  redness,  and  dry  chlorine  is  then  passed  through 
(Fig.  119).  Carbon  monoxide  and  aluminium  chloride  are 


FIG.  119. 

formed,  and  the  latter,  being  volatile,  must  be  condensed  in  a  bottle 
surrounded  with  cold  water. 


A12Q3  + 

Aluminium  oxide. 


3C 


3C12 


SCO 


+          2A1C15 

Aluminium  chloride. 


The  purified  chloride  is  a  snow-white  crystalline  compound, 
which  vaporizes  without  melting  at  a  temperature  of  about  183°. 
When  thrown  into  water,  it  dissolves  and  combines  with  the 


ALUMINIUM    SULPHATE.  303 

liquid,  forming  a  hydrate,  which  cannot  be  dried  without  decom- 
position. It  slowly  absorbs  moisture  from  the  air,  giving  off 
hydrochloric  acid  while  aluminium  oxide  is  formed. 

The  vapor  density  of  the  chloride  below  440°  corresponds  to 
the  formula  APC16 ;  above  that  temperature  it  diminishes,  and 
at  850°  it  is  that  required  by  the  formula  A1CP. 

508.  ALUMINIUM    OXIDE,  A1203. — This  compound   is   com- 
monly called  alumina.     It  is  found  native  in  corundum,  ruby, 
sapphire,  oriental  topaz,  and  emery  :  the  black  color  of  emery  is  due 
to  the  presence  of  oxide  of  iron.     Aluminium  oxide  may  be  ob- 
tained in  the  laboratory  by  heating  the  aluminium  hydrate  which 
is  thrown  down  as  a  gelatinous  white  precipitate  when  ammonia 
is  added  to  a  solution  of  alum.     It  then  forms  a  white  powder, 
which  is  infusible  except  in  the  oxyhydrogen  flame  and  in  the 
electric  arc.     It  is  not  reducible  by  hydrogen,  and  carbon  de- 
oxidizes it  only  in  the  electric  furnace.     The  crystallized  varie- 
ties of  alumina  are  used  as  gems :  ruby  is  red,  sapphire  is  blue, 
and  topaz  is  yellow.     By  reason  of  their  hardness,  corundum 
and  emery  are  of  great  value  in  grinding  and  polishing  glass, 
steel,  and  metals. 

Aluminium  hydroxide,  Al(OH)3,  forms  a  bulky  gelatinous  pre- 
cipitate when  ammonia-water  or  an  alkaline  hydroxide  or  carbonate 
is  added  to  a  solution  of  alum  or  any  salt  of  aluminium.  The 
hydroxides  AIO(OH)2  and  APO(OH)4  constitute  the  minerals 
bauxite  and  diaspore. 

509.  ALUMINIUM  SULPHATE,  AP(S04)3. — When  aluminium 
hydroxide,  either  bauxite  or  that  obtained   from   cryolite  (see 
§  240),  is  dissolved  in  sulphuric  acid,  and  the  solution  evaporated, 
a  white   crystalline    mass  of  aluminium   sulphate   is   obtained. 
From  its  aqueous  solution  this  salt  deposits  in  small  pearly  scales 
containing  eighteen  molecules  of  water  of  crystallization.     It  is 
soluble  in  twice  its  weight  of  cold  water,  and  is  used  as  a  mordant 
in  dyeing,  for  it  may  be  decomposed  in  the  fibres  of  the  tissues  to 
be  dyed,  and  the  fine  particles  of  aluminium  oxide  deposited  firmly 
fix  the  color  in  the  fabric.    For  this  purpose  it  is  usually  first  con- 
verted into  aluminium  acetate  by  the  addition  of  calcium  acetate. 


304  LESSONS    IN    CHEMISTRY. 

When  aluminium  sulphate  is  heated,  it  first  loses  ito  water  of 
crystallization,  and  then  gives  off  sulphur  trioxide,  leaving  a  resi- 
due of  aluminium  oxide. 

Al2(SO*)a  3S03  +  A1203 

510.  ALUMS. — To  a  cold  saturated  solution  of  aluminium  sul- 
phate, we  add  a  cold  saturated  solution  of  potassium  sulphate,  and 
stir  the  mixture.  A  crystalline  deposit  forms.  The  two  salts 
have  combined  to  form  a  double  salt,  which  is  called  an  alum.  It 
crystallizes  with  twenty-four  molecules  of  water  of  crystallization, 
and  its  formula  is  AP(SO*)3.K2S04  -f  24H20.  By  the  substitu- 
tion of  sodium  sulphate  or  ammonium  sulphate  for  the  potassium 
sulphate  in  the  preceding  experiment,  sodium  alum  or  ammonium 
alum  will  be  formed.  The  compositions  of  these  substances  are 
precisely  analogous  to  that  of  the  potassium  alum,  and  they  crys- 
tallize in  the  same  form,  which  is  the  regular  octahedron. 

A12(S04)3.Na2S04     -r     24H20     Sodium  alum. 
A12(SO*)3.(NH*)2SO*     +     24H20     Ammonium  alum. 

Potassium  alum  is  soluble  in  about  thirty  times  its  weight  of  cold  water,  and 
in  less  than  one-third  its  weight  of  boiling  water.  It  forms  voluminous,  trans- 
parent crystals  when  the  hot  saturated  solution  is  allowed  to  cool.  When 
heated,  it  melts  in  its  water  of  crystallization,  which  is  afterwards  driven  off; 
the  salt  increases  enormously  in  volume,  and  the  anhydrous  alum  then  forms 
a  white,  porous  mass.  Alum  may  be  obtained  crystallized  in  cubes  by  adding 
a  very  small  quantity  of  potassium  carbonate  or  hydrate  to  its  hot  solution  and 
allowing  it  to  cool. 

Sodium  alum  is  very  soluble  in  cold  water,  and  is  not  employed  in  the  arts. 

Ammonium  alum  is  the  compound  ordinarily  called  alum.  Its  solubility  is 
about  the  same  as  that  of  potassium  alum.  When  it  is  strongly  heated,  it 
leaves  a  residue  of  pure  alumina. 

Other  metals  whose  oxides  are  analogous  in  constitution  to  aluminium  oxide, 

form  alums  having  compositions  and  general  properties  like  those  of  ordinary 

alum.    These  alums  are  isomorphous.     Although  their  colors  be  different,  they 

may  be  mixed  in  the  same  crystal,  and   the  form   of  the  latter  will  remain 

unchanged.     Thus,  chromium  alum  is  red :   when  one  of  its  red  octahedral 

crystals  is  immersed  in  a  saturated  solution  of  potassium  alum  and  the  water 

is  allowed  to  evaporate,  the  octahedron  will  grow  larger,  and  the  red  chromium 

alum  will  be  surrounded  by  the  colorless  potassium  alum.     The  compositions 

of  three  of  these  alums  are  shown  by  the  following  formulae : 

Iron  alum,  Fe2(S04)3.K2SO*       +     24H20 

Manganese  alum,  Mn2(SO*)3.K2SO*     +     24IPO 

Chromium  alum,    Cr2(S04)3.K2SO*       +     24H20 


CLAY    AND    POTTERY.  305 

511.  CLAY  AND  POTTERY. — The  feldspars — orthoclase,  albite, 
and  labradorite — are  double  silicates  of  aluminium  and  potas- 
sium, sodium  and  calcium.  The  micas  and  garnets  are  also 
double  silicates  of  aluminium  and  various  other  metals.  The  dis- 
integration of  these  minerals  by  the  action  of  air  and  frost  results 
in  the  formation  of  clays,  and  the  nature  of  a  clay  will  depend  on 
that  of  the  rock  from  which  it  is  derived.  The  purest  clay  is  a 
hydrated  silicate  of  aluminium  known  as  kaolin,  or  porcelain  clay. 
It  contains  Al203.2Si02.2H20.  Clays  which  form  a  coherent  mass 
when  mixed  with  water,  and  which  when  calcined  become  very 
hard  without  being  fused,  are  called  plastic  clays,  and  are  used  for 
the  manufacture  of  bricks,  fire-brick,  pottery,  etc.  Fuller's  earth 
is  a  kind  of  clay  of  which  the  paste  is  not  strongly  coherent :  it  is 
used  in  scouring  and  fulling  cloths.  Marls  are  mixtures  of  clay 
and  chalk,  generally  of  a  greenish  color,  and  often  found  in  large 
deposits :  they  are  used  as  fertilizers  for  sandy  soils. 

Porcelain  is  made  from  a  mixture  of  the  finest  kaolin  with  a 
little  finely-powdered  sand  and  feldspar,  which  are  added  to  pre- 
vent the  mass  from  shrinking  and  to  render  the  ware  translucent 
by  undergoing  partial  fusion.  The  greatest  care  is  exercised  that 
the  materials,  which  are  made  into  a  paste  with  water,  may  be 
intimately  mixed ;  after  the  articles  have  been  fashioned  from  the 
perfectly  homogeneous  paste,  they  are  baked  at  a  dull  red  heat,  and, 
after  cooling,  are  removed  from  the  furnace.  They  are  then  dipped 
into  water  holding  in  suspension  a  mixture  of  kaolin  and  quartz  in 
an  impalpable  powder.  This  powder  fills  the  pores  on  the  surface, 
and  when  the  articles  are  again  baked  the  mixture  fuses  and  forms 
a  transparent  glaze,  while  the  whole  mass  becomes  partially  vitrified. 

Stoneware  is  manufactured  from  a  kaolin  which  is  not  sufficiently 
pure  for  porcelain-making.  It  is  baked  at  one  operation,  and  when 
the  temperature  of  the  oven  is  very  high  a  little  common  salt  is 
thrown  on  the  incandescent  objects;  by  the  action  of  the  hydrogen 
compounds  in  the  flame,  hydrochloric  acid  is  formed,  while  the 
sodium  forms  a  double  silicate  with  aluminium  on  the  surface  of 
the  ware.  This  silicate,  being  quite  fusible,  melts  and  spreads  out 
on -the  surface  of  the  ware,  forming  an  even  glaze. 

20 


306  LESSONS    IN   CHEMISTRY. 

Articles  of  faience  are  made  from  a  still  more  common  clay 
mixed  with  finely-powdered  quartz,  and,  after  being  rendered  cohe- 
rent by  a  preliminary  baking,  are  coated  with  a  mixture  of  pow- 
dered quartz,  potassium  carbonate,  and  lead  oxide.  This  mixture 
fuses  to  a  transparent  varnish  when  the  articles  are  baked  a  second 
time,  and  various  colors  are  obtained  by  the  addition  of  certain 
metallic  oxides.  Oxide  of  tin  renders  the  glaze  white  and  opaque. 

The  glazing  of  pottery  intended  for  culinary  purposes  should 
contain  no  lead,  as  lead  silicate  is  attacked  by  dilute  vegetable 
acids,  and  a  lead  salt  is  sometimes  so  formed  in  articles  of  food. 

The  blue  pigment  ultramarine  is  made  by  heating  kaolin  with  sodium  sul- 
phate, sodium  carbonate,  sulphur,  charcoal,  and  rosin  :  the  semi-vitrified  mass 
is  then  pulverized,  roasted,  again  pulverized,  washed  and  dried.  The  mineral 
lapis  lazuli  is  natural  ultramarine. 

512.  TESTS  FOR  ALUMINIUM. — Solutions  of  aluminium  salts 
usually  have  an  acid  reaction.  The  alkaline  hydroxides  and  am- 
monia produce  gelatinous  white  precipitates  of  aluminium  hydrox- 
ide, soluble  in  acids  and  in  the  alkaline  hydroxides.  The  same 
precipitate  is  thrown  down  by  the  alkaline  carbonates  and  by  am- 
monium sulphide,  carbon  dioxide  being  liberated  by  the  former 
and  hydrogen  sulphide  by  the  latter. 
A12(S04)3  +  3(NH4)2S  +  6H20  =  2A1(OH)3  +  3(NH4)2SO*  +  3H2S 

When  an  aluminium  salt  or  aluminium  oxide  is  strongly  heated 
in  a  blow-pipe  flame,  and  the  resulting  white  mass  is  moistened 
with  a  drop  of  cobalt  nitrate  solution  and  again  heated,  it  be- 
comes sky-blue,  without  fusion. 

513.  Closely  related  to  aluminium  by  chemical  analogies  are  a  number  of 
.•are  metals,  of  which  three  have  been  obtained  in  the  metallic  state.  They  are 
cerium,  didymium,  and  lanthanum.  As  silicates  and  phosphates  they  occur  in 
cerite,  gadolinite,  monazite,  and  other  rare  minerals :  didymium  has  been 
resolved  into  two  components, — neodymium  and  praseodymium. 

Scandium,  samarium,  holmium,  erbium,  thulium,  ytterbium,  and  yttrium  are 
elements  which  have  not  been  obtained  in  the  metallic  state ;  but  their  oxides 
have  been  isolated  in  small  quantities,  and  a  few  of  their  salts  have  been 
studied.  Each  of  these  elements  is  distinctly  characterized  by  its  spectrum, 
which  is  an  unquestionable  indication  of  the  individuality  of  the  element. 
All  these  elements  appear  to  form  sesquioxides,  and  their  chlorides,  which 
have  been  prepared,  contain  one  atom  of  metal  and  three  of  chlorine,  cor- 
responding in  composition  to  aluminium  chloride. 


IRON    AND    ITS    METALLURGY.  307 


LESSON    LVIII. 
IRON  AND  ITS  METALLURGY. 

514.  Iron  is  found  in  the  metallic  state  in  meteoric  stones,  which 
are  occasionally  drawn  to  the  earth  during  its  passage  through  space. 

The  more  important  minerals  from  which  iron  is  extracted 
are  magnetite,  Fe304 ;  hematite,  or  specular  iron,  Fe203 ;  limonite, 
or  brown  hematite,  2Fe203  -f  3H2O ;  goethite,  Fe203  +  H20 ; 
and  siderite,  or  spathic  iron,  FeCO3.  Iron  pyrites,  which  is 
chiefly  employed  for  the  manufacture  of  sulphuric  acid,  is  the 
disulphide  FeS2.  Some  of  the  minerals  are  found  in  a  tolerably 
pure  condition,  but  generally  they  are  mixed  with  silicious  mat- 
ters, clay,  limestone,  coal,  etc.  When  the  ore  contains  sulphur, 
it  is  first  roasted,  and  the  sulphur  is  burned  into  sulphur  dioxide, 
while  the  iron  remains  as  oxide.  Very  frequently  also  the  ores 
are  calcined  to  expel  water  and  carbon  dioxide,  and  to  render 
them  more  porous. 

The  oxide  of  iron,  either  the  natural  ore  or  produced  by  the 
roasting,  is  reduced  by  being  heated  with  charcoal.  A  rather  primi- 
tive method,  but  one  which  for  ages  furnished  all  of  the  iron  em- 
ployed, and  which  is  still  used  for  the  reduction  of  very  rich  ores, 
is  known  as  the  Catalan  method,  the  name  being  derived  from 
the  Spanish  province  in  which  the  process  is  still  carried  on.  It 
consists  in  piling  the  ore  and  charcoal  in  two  heaps,  side  by  side, 
on  burning  charcoal  contained  in  the  hearth  of  a  furnace  where 
the  combustion  is  sustained  by  a  blast  of  air  from  the  tuyere  of  a 
bellows  (Fig.  120).  The  reduced  iron  collects  on  the  hearth  in  a 
spongy  mass,  which  is  removed  and  directly  submitted  to  the 
operation  of  forging.  The  silicious  matters  of  the  ore  combine 
with  a  portion  of  ferrous  oxide  produced  during  the  operation,  and 
form  a  very  fusible  slag,  consisting  of  ferrous  silicate. 

515.  The  blast-furnace  process  for  the  reduction  of  iron  is 


308 


LESSONS    IN   CHEMISTRY. 


applicable  to  all  iron  ores,  and  the  fuel  employed  is  either  char- 
coal,  coke,  or  anthracite.  The  blast-furnace  is  a  tall  column  of 
considerable  height,  sometimes  almost  cylindrical,  but  more  often 

constructed  in  the  form  of  a 
double  frustum  of  cones  placed 
base  to  base  (Fig.  121).  It  is 
lined  with  infusible  fire-brick; 
the  hearth  is  flat,  and  inclines 
very  slightly  towards  the  front, 
which  is  so  arranged  that  the 
molten  iron  may  be  drawn  off 
at  the  bottom  through  a  hole 
which  is  kept  closed  with  a  clay 
plug,  and  the  slag  may  be  re- 
moved as  it  accumulates  and 
floats  on  the  surface  of  the  liquid 
iron.  During  the  reduction,  the 
bottom  of  the  furnace  is  closed, 
and  a  blast  of  air  is  injected 
through  tuyere  pipes  (T)  by 
powerful  blowing  engines.  Coal, 

ore,  and  limestone  are  continually  supplied  in  alternate  layers  at  the 
open  top  of  the  furnace,  and  in  the  interval  between  the  introduc- 
tion of  these  materials  the  top  is  closed  by  a  conical  cap  or  dome, 
which  can  be  readily  moved  by  suitable  machinery.  At  the  be- 
ginning of  the  operation  the  furnace  is  heated  by  a  supply  of  com- 
bustibles only,  and,  when  the  temperature  has  been  sufficiently 
raised,  the  ore  and  limestone  are  gradually  alternated  with  the 
introduction  of  coal,  until  the  furnace  is  completely  filled.  By 
the  combustion  of  the  coal  immediately  above  the  tuyeres,  carbon 
dioxide  is  produced,  but  as  this  comes  in  contact  with  the  highly- 
heated  coal  it  is  reduced  to  carbon  monoxide :  as  the  latter  gas 
rises  through  the  mixture,  it  reduces  the  oxide  of  iron,  and  the 
metallic  iron  formed  is  disseminated  in  small  particles  through  the 
mass  of  reduced  ore.  As  the  materials  descend  in  the  furnace, 
the  silicious  matters  of  the  ore,  and  the  lime  resulting  from  the 


FIG.  120. 


BLAST-FURNACE   PROCESS. 


309 


action  of  the  heat  on  the  limestone,  unite  to  form  a  very  fusible 
slag  of  calcium  and  aluminium  silicate,  while  the  particles  of  iron 
are  agglomerated  together,  and,  together  with  the  slag,  flow  to  the 
hearth  of  the  furnace.  The  gases  produced  during  the  operation 
contain  a  large  proportion  of  carbon  monoxide ;  they  are  carried 


FIG.  121. 

off  by  pipes  inserted  near  the  top  of  the  furnace,  and  their  com- 
bustion furnishes  heat  for  the  boilers  which  supply  steam  to  the 
blowing  engines  and  to  furnaces  containing  long  series  of  pipes, 
through  which  the  air  from  the  engines  is  forced  before  it  enters 
the  tuyeres.  The  blast  is  heated  as  highly  as  possible,  for  by  the 
use  of  hot  air  a  very  great  saving  is  effected  in  the  quantity  of 
fuel  required. 


310  LESSONS    IN    CHEMISTRY. 

When  a  sufficient  quantity  of  iron  has  accumulated  on  the 
hearth  of  the  furnace,  the  blowing  engines  are  slowed  or  stopped, 
and  by  picking  out  the  clay  plug  the  molten  iron  is  caused  to  flow 
into  semi-cylindrical  channels  in  sand  on  the  floor  of  the  casting- 
room.  Blows  from  a  sledge-hammer  detach  the  bars  of  iron  so 
formed  from  that  in  the  channel  from  which  the  moulds  are  filled, 
and  they  constitute  pig-iron. 

This  iron  contains  carbon  and  smaller  proportions  of  silicon, 
sulphur,  and  phosphorus,  which  are  derived  from  the  various 
materials  in  the  blast-furnace.  These  impurities  are  in  great  part 
removed  by  melting  the  iron  in  puddling-furnaces,  where  the 
carbon  and  silicon  are  oxidized  either  by  air,  or  better  by  oxygen 
derived  from  pure  magnetic  iron  ore,  or  from  scales  of  black  oxide 
of  iron  obtained  in  another  operation.  During  the  process,  the 
molten  iron  is  vigorously  stirred  until  it  is  converted  into  a  spongy 
mass,  which  is  then  removed  and  placed  under  a  steam-hammer, 
by  the  blows  of  which  all  the  ferrous  silicate  and  black  oxide  of 
iron  formed  during  the  process  of  puddling  are  squeezed  out,  while 
a  Uoom  of  soft  iron  remains.  The  ferruginous  scoriae  or  ashes 
obtained  in  this  operation  are  used  in  refining  a  new  quantity  of 
cast-iron. 

516.  The  soft  iron  of  commerce,  known  as  wr  ought-iron,  is 
not  perfectly  pure.  It  contains  traces  of  carbon,  silicon,  sulphur, 
phosphorus,  nitrogen,  and  sometimes  other  elements.  Pure  iron 
may  be  obtained  by  passing  hydrogen  over  pure  ferric  chloride 
heated  to  bright  redness  in  a  porcelain  tube.  Hydrochloric 
acid  is  disengaged,  and  the  iron  remains  as  an  almost  infusible, 
spongy  mass.  By  passing  dry  hydrogen  over  ferric  oxide  heated 
to  dull  redness  in  a  glass  bulb  (Fig.  122),  metallic  iron  is  ob- 
tained as  a  dull  black  powder,  in  which  form  it  becomes  oxidized 
with  great  readiness.  If  a  lighted  match  be  applied  to  a  single 
point  in  recently-prepared  iron  reduced  by  hydrogen,  the  whole 
mass  quickly  takes  fire  and  burns  into  ferric  oxide.  By  reducing 
the  ferric  oxide  at  a  temperature  below  redness,  a  powder  of 
iron  may  be  obtained  which  will  even  take  fire  spontaneously  on 
contact  with  the  air. 


STEEL. 


311 


The  composition  and  general  properties  of  cast-iron  vary 
greatly,  for  while  cast-iron  always  contains  silicon  and  carbon, 
these  elements  are  only  in  part  chemically  combined  with 
the  iron.  The  proportion  of  carbon  varies  from  2  to  5.5  per  cent. 
When  cast-iron  containing  a  large  proportion  of  carbon  is  rapidly 
cooled,  it  becomes  hard  and  brittle,  and  its  fracture  is  coarse,  crys- 
talline, and  very  white.  It  is  called  white  iron.  When,  however, 
such  iron  is  allowed  to  cool  slowly,  a  considerable  quantity  of  the 


FIG.  122. 

carbon  separates  as  shining  scales  of  graphite,  and  the  iron  is  then 
softer,  has  a  closer  structure,  and  a  gray  fracture.  It  is  called 
gray  iron.  Iron  containing  sulphur  and  phosphorus  is  always 
white ;  phosphorus  renders  iron  brittle  while  cold,  and  sulphur 
renders  it  brittle  while  hot.  In  the  first  case  the  iron  is  said  to 
be  cold-short,  while  in  the  second  it  is  called  red-short. 

Spiegeleisen  and  ferro-manganese  are  varieties  of  cast-iron 
very  rich  in  carbon,  and  containing  much  manganese.  They 
are  employed  in  the  manufacture  of  steel.  Spiegel  is  crystal- 
line, and  breaks  with  smooth  and  highly-lustrous  surfaces. 

517.  Steel  is  iron  containing  from  0.2  to  2  per  cent,  of  carbon, 
and  traces  of  nitrogen.  It  is  obtained  by  a  number  of  processes, 
which  depend  either  on  the  partial  decarbonization  of  cast-iron  or 
on  the  introduction  of  the  required  proportion  of  carbon  into  soft 


312 


LESSONS    IN   CHEMISTRY. 


iron.  When  manganiferous  cast-iron  is  maintained  for  a  time 
melted  under  a  layer  of  magnetic  iron  ore  or  ferruginous  scoriae, 
and  the  operation  is  arrested  at  the  proper  moment,  the  iron  still 
retains  a  certain  proportion  of  carbon,  and  natural  steel  is  obtained. 
Cement-steel,  or  blister-steel,  is  made  by  piling  soft-iron  bars 
between  layers  of  charcoal  in  fire-clay  boxes,  which  are  then 
heated  to  redness  in  a  furnace,  and  the  temperature  is  maintained 
for  several  days  ;  the  iron  absorbs  a  certain  proportion  of  carbon, 
and  is  converted  into  steel.  As,  however,  the  exterior  of  the  bars 
will  necessarily  contain  more  carbon  than  the  interior,  the  metal 
is  rendered  homogeneous  by  being  melted  in  crucibles  heated  in  a 
powerful  wind-furnace.  It  then  constitutes  cast-steel. 

The  most  important  method  of  manufacture  of  steel  is  named, 
from  its  inventor,  the  Bessemer  process.  It  consists  in  completely 
decarbonizing  cast-iron  and  then  adding  sufficient  cast-iron  of  the 
proper  quality  to  give  to  the  whole  mixture  the  desired  proportion 
of  carbon.  The  operation  is  conducted  in  oval  vessels  of  strong 

iron  plate  lined  with  infusi- 
ble fire-brick.  This  appa- 
ratus, which  is  called  a 
converter,  is  supported  on 
trunnions,  so  that  it  may 
swing  back  and  forward  on 
a  horizontal  axis.  One  of 
the  trunnions  is  hollow,  and 
communicates  with  a  pipe 
passing  partly  around  the 
converter  and  then  leading 
to  its  bottom  ;  the  fire-brick 
is  here  pierced  with  a 
number  of  holes,  so  that  a 
blast  of  air  may  be  forced 
UP  through  the  contents  of 
the  converter  (Fig.  123). 

The  plant,  as  the  whole  of  any  manufactory  is  called,  is  established 
near  blast-furnaces,  and  cupola  furnaces,  for  melting  the  pig-iron, 


123 


BESSEMER  STEEL  PROCESS.  313 

are  constructed  near  the  converter.  Everything  being  ready, 
burning  wood  is  thrown  into  the  converter,  which  is  then  partly 
filled  with  coke,  and  the  blast  is  turned  on  so  that  the  fire-brick 
lining  is  heated  to  whiteness.  The  converter  is  then  inverted ; 
the  coke  is  dumped  out,  and  molten  iron  is  run  in  from  cupola 
furnaces.  During  the  filling,  the  converter  is  kept  in  an  inclined 
position,  so  that  the  tuyeres  for  the  passage  of  the  blast  may  not 
become  filled  with  the  molten  iron.  The  blast,  which  is  under 
strong  pressure,  is  now  turned  on,  .and  the  converter  is  rotated 
to  an  upright  position.  As  the  air  bubbles  up  through*  the  iron, 
the  carbon,  silicon,  and  other  oxidizable  elements  present  are  con- 
sumed, and  a  brilliant  flame  rushes  with  a  roaring  noise  from  the 
mouth  of  the  converter.  When  the  carbon  of  the  iron  is  burned 
out,  the  appearance  of  the  flame  undergoes  a  change  which  informs 
the  workmen  of  the  termination  of  the  operation.  The  converter 
is  then  inclined,  and  the  blast  is  arrested.  In  the  mean  time,  the 
quantity  of  iron  in  the  charge  being  accurately  known,  the  exact 
quantity  of  Spiegel  required  to  convert  the  charge  into  steel  has 
been  melted  in  another  cupola  furnace  :  the  blast  is  stopped,  the 
molten  spiegel  run  into  the  converter,  and  the  blast  turned  on 
for  a  moment  in  order  that  the  contents  may  be  perfectly  mixed. 
The  steel  is  then  poured  out  into  an  enormous  ladle,  which  is 
carried  by  a  revolving  crane  over  the  circumference  of  a  circle 
around  which  are  arranged  ingot-moulds,  into  which  the  steel  is 
cast. 

A  modification  of  the  Bessemer  process,  known  as  the  basic  pro- 
cess, is  extensively  used  in  Europe  for  making  steel  from  pig- 
iron  rich  in  phosphorus.  The  fire-brick  lining  of  the  converter 
is  replaced  by  one  of  dolomite,  the  bases  of  which  aid  in  the  oxi- 
dation and  removal  of  the  phosphorus  by  forming  phosphates. 
These  constitute  a  slag  valued  as  a  fertilizer  in  agriculture. 

The  Siemens  regenerative  furnace  (see  $  468)  has  been  successfully  applied 
in  the  production  of  steel  by  a  process  which  is  analogous  to  "puddling," 
and  known  as  the  Siemens-Martin  or  "  open  hearth  "  process.  It  consists  in 
melting  on  a  hearth  lined  with  fire-brick  or  basic  material  a  quantity  of  cast- 
iron,  and  then  adding  at  intervals  wrought-iron  and  iron  ores  to  reduce  the 
carbon  to  the  desired  proportion. 


314  LESSONS    IN    CHEMISTRY. 

518.  The  valuable  qualities  of  steel  depend  upon  the  ease  with 
which  it  can  be  hardened  or  softened  at  pleasure,  and  the  opera- 
tions by  which  the  change  in  hardness  is  brought  about  consti- 
tute the  processes  of  tempering.  When  heated  and  allowed  to 
cool  slowly,  steel  becomes  soft  and  malleable  like  soft  iron,  but  if 
it  be  heated  to  redness  and  then  suddenly  cooled  by  plunging  it 
into  cold  water,  it  is  rendered  hard  and  brittle  ;  it  is,  however, 
still  elastic.  Intermediate  degrees  of  hardness  are  obtained  by 
re-heating  to  temperatures  depending  on  the  desired  hardness. 
Part  of  the  temper  is  then  said  to  be  drawn.  The  color  which 
the  surface  of  the  metal  assumes  is  an  index  of  the  temperature. 

Straw  yellow  corresponds  to  230°. 
Brown  "  255°. 

Light  blue  "  285-290°. 

Indigo  blue  "  295°. 

Sea  green  "  331°. 

We  may  very  well  study  the  phenomena  of  tempering  by  heat- 
ing a  steel  wire  or  a  piece  of  watch-spring  to  redness  and  quickly 
immersing  it  in  water.  It  is  now  very  hard  and  brittle  ;  it  breaks 
as  readily  as  a  piece  of  glass.  We  again  heat  it  gently  until  its 
surface  becomes  of  a  blue  color,  and  now,  whether  we  dip  it  in 
water  or  allow  it  to  cool  slowly,  we  will  find  that  it  has  become 
quite  elastic,  but  is  still  hard.  When,  however,  we  heat  it  to  red- 
ness and  allow  it  to  cool  slowly,  it  becomes  soft  and  flexible ;  it 
will  not  break,  but  will  retain  any  form  into  which  it  is  bent. 

The  process  of  casehardening,  which  is  applied  to  inferior 
kinds  of  cutlery,  consists  in  embedding  the  objects,  which  are 
made  of  soft  iron,  in  charcoal  contained  in  crucibles  or  clay  boxes. 
These  are  then  heated  to  bright  redness,  and  the  surface  of  the 
iron  becomes  converted  into  steel. 

Steel  is  less  fusible  than  cast-iron,  but  much  more  fusible  than 
soft  iron ;  at  the  temperature  at  which  soft  iron  becomes  pasty, 
steel  melts. 


IRON   AND    ITS   COMPOUNDS.  315 

LESSON    LIX. 
IRON  AND   ITS  COMPOUNDS. 

519.  The  density  of  soft  iron  varies  from  7.4  to  7.9.  It  is 
ductile,  malleable,  and  very  tenacious.  It  fuses  only  at  the  highest 
temperatures  of  a  powerful  wind-furnace,  but  at  a  high  white 
heat  it  becomes  so  soft  that  two  pieces  of  the  metal  may  be  readily 
united  in  a  solid  mass  by  hammering  or  by  pressure :  the  opera- 
tion is  called  welding.  At  a  somewhat  lower  temperature  it  may 
be  readily  rolled  into  sheets  or  bars,  and  sheet-iron  is  made  by 
passing  the  heated  metal  between  polished  steel  rollers.  Iron  may 
be  rolled  into  leaves  as  thin  as  paper.  Tin  plate  is  sheet-iron 
covered  with  a  coating  of  tin.  Galvanized  iron  is  made  by  dipping 
perfectly  clean  sheet-iron  into  melted  zinc. 

Iron  is  attracted  by  a  magnet,  and  becomes  itself  a  magnet 
while  under  the  magnetic  influence,  but  loses  its  magnetism  when 
the  exciting  cause  is  removed.  Under  the  same  circumstances 
steel  becomes  a  permanent  magnet. 

Unless  in  a  state  of  fine  division,  iron  is  unaffected  by  dry  air 
at  temperatures  below  redness,  but  at  a  red  heat  it  combines  with 
oxygen  and  is  converted  into  a  black  oxide  which  forms  scales  on 
its  surface.  It  is  rapidly  rusted  by  moist  air,  and  the  rust  is  a 
hyd  rated  ferric  oxide. 

When  the  formation  of  rust  has  begun,  it  proceeds  with  great  rapidity,  and 
if  the  mass  of  iron  be  of  sueh  a  form  that  a  large  surface  is  combined  with  a 
comparatively  small  bulk,  as  in  a  long  coil  of  wire  or  mass  of  small  scrap  iron 
partly  immersed  in  water,  the  temperature  may  be  much  elevated  by  the  rust- 
ing. It  appears  that  hydrogen  dioxide  is  formed  during  the  rusting  of  iron,  and 
that  substance  would  greatly  accelerate  the  change :  the  nitrogen  of  the  air 
also  plays  some  part  in  the  phenomenon,  for  rust  always  contains  a  trace  of 
ammonia. 

At  a  red  heat,  iron  decomposes  water,  liberating  hydrogen,  and 
forming  an  oxide.  It  is  dissolved  by  hydrochloric  and  sulphuric 
acids,  hydrogen  being  set  free ;  this  hydrogen  has  an  unpleasant 


316  LESSONS    IN   CHEMISTRY. 

odor,  probably  due  to  carbon  compounds  formed  by  the  action 
of  the  carbon  of  the  iron.  Dilute  nitric  acid  also  dissolves  iron, 
disengaging  red  vapors,  but  the  strongest  nitric  acid  does  not 
affect  it. 

If  some  clean  iron  wire  or  some  bright  nails  be  dropped  into 
pure  nitric  acid,  or  a  mixture  of  strong  nitric  and  sulphuric 
acids,  no  action  takes  place ;  the  iron  may  now  be  removed  and 
placed  in  more  dilute  acid,  and  even  here  it  will  not  dissolve :  it 
is  said  to  be  in  the  passive  state.  Other  oxidizing  agents  produce 
a  like  effect :  it  is  supposed  that  the  iron  becomes  covered  with 
a  film  of  oxide,  which  protects  it  from  further  action  of  the  acid. 

Iron  forms  two  series  of  compounds, — ferric  compounds,  in 
which  the  iron  is  triatomic,  and  ferrous  compounds,  in  which  it 
plays  the  part  of  a  diatomic  element.  Under  certain  conditions 
two  atoms  of  iron  act  as  a  hexatomic  couple. 

520.  FERROUS  CHLORIDE,  FeCl2,  is  made  by  passing  dry  hydro- 
chloric acid  gas  over  metallic  iron  heated  to  redness  in  a  porcelain 
tube.     It  then  condenses  in  white,  pearly  scales  in  the  cooler  part 
of  the  tube. 

A  solution  of  ferrous  chloride  may  be  obtained  by  dissolving  iron  in  hydro- 
chloric acid.  \Vhen  the  filtered  liquid  is  sufficiently  evaporated,  it  deposits 
bluish-green  crystals  in  which  every  molecule  of  ferrous  chloride  is  combined 
with  four  molecules  of  water. 

521.  FERRIC  CHLORIDE,  FeCl3,  sublimes  in  brilliant  violet 
crystals  when  chlorine  is  passed  over  incandescent  iron  con- 
tained in  a  glass  or  porcelain  tube.     It  is  very  soluble  in  water, 
but  its  solution  undergoes  a  curious  change  by  boiling.     A  solu- 
tion of  ferric  chloride  is  obtained  by  dissolving  ferric  oxide  in 
hot  hydrochloric  acid.     When  this  solution  is  evaporated  at  a 
low    temperature,  the   hydrated  ferric    chloride    remains  as  a 
brownish-yellow,  deliquescent  mass,  but  when  the   solution  is 
boiled  its  color  darkens,  and  the  reactions  and  general  properties 
of  the  liquid  seem  to  show  that  it  has  been  decomposed  into 
hydrochloric  acid    and  a  soluble  variety  of  ferric   hydroxide. 
Above  700°  the  vapor  density  of  ferric  chloride  corresponds  to 

.the  formula  FeCl3,  but  at  450°  it  is  that  required  by  Fe2Cl6. 


OXIDES   OF   IRON.  317 

522.  FERROUS  OXIDE,  FeO,  has  been  obtained  as  a  black  powder  by  passing 
a  mixture  of  carbon  dioxide  and  carbon  monoxide  in  equal  volumes  over  heated 
ferric  oxide,,     Carbon  monoxide  alone  wotild  yield  metallic  iron. 

523.  FERRIC  OXIDE,  Fe203,  constitutes  the  minerals  known  as 
red  hematite  and  specular  iron.    It  is  obtained  as  a  fine  red  powder 
by  strongly  heating  ferrous  sulphate  in  a  crucible  :  sulphur  dioxide 
and  sulphur  trioxide  are  disengaged,  while  ferric  oxide  remains. 

2FeS04    =     SO2     +     SO3     +     Fe203 

This  powder  is  very  hard,  and  is  used  for  polishing  under  the 
names  jewellers'  rouge  and  colcoihar. 

When  an  alkaline  hydroxide  or  ammonia  is  added  to  a  solution 
of  ferric  chloride,  a  flocculent,  brown  precipitate  of  ferric  hydrox- 
ide, Fe(OH)3,  is  thrown  down.  This  is  the  precipitate  which, 
after  being  thoroughly  washed,  is  the  proper  antidote  for  poison- 
ing by  arsenious  oxide.  Ferric  solutions  containing  tartaric  acid 
are  not  precipitated  by  the  alkaline  hydroxides. 

Rust  is  a  ferric  hydroxide  of  which  the  composition  usually  corresponds  with 
the  formula  (Fe203)23H20  =  2Fe(OH)3  +  Fe203.  This'is  also  the  composition 
of  the  natural  hydrate  brown  hematite.  Goethite  is  a  hydroxide  having  the 
composition  Fe'03.H20  =  2FeO(OH). 

There  is  a  soluble  modification  of  ferric  hydroxide.  It  may  be  obtained  by 
pouring  a  solution  of  ferric  chloride  which  has  been  heated  to  100°  into  the 
inner  vessel  of  a  dialyser  ($  220),  the  water  in  the  exterior  vessel  being  fre- 
quently changed.  Hydrochloric  acid  passes  through  the  membrane,  while  a 
solution  of  ferric  hydroxide  remains  within.  Dialysis  of  a  solution  of  ferric 
acetate  yields  soluble  ferric  hydroxide  in  the  same  manner.  This  solution  is 
used  in  medicine  under  the  name  dialysed  iron. 

524.  FERROSO-FERRIC  OXIDE,  Fe30*,  is  magnetic  oxide  of  iron, 
commonly  called  black  oxide  of  iron.     It  is  found  native  in  large 
quantities  in  the  neighborhood  of  Lake  Superior.     It  forms  in 
black  scales  on  the  surface  of  iron  heated  to  redness  in  the  air.    It 
is  attracted  by  the  magnet.    It  is  a  compound  of  ferrous  and  ferric 
oxides,  Fe304  =  FeO.Fe203. 

525.  FERROUS  SULPHIDE,  FeS,  so  largely  used  in  the  labora- 
tory for  the  preparation  of  hydrogen  sulphide,  is  made  by  heating 
a  mixture  of  iron  filings  with  two-thirds  its  weight  of  sulphur  to 
redness  in  a  covered  crucible.     After  fusion,  the  mass  is  poured 
out,  and  on  cooling  forms  a  black  solid  of  a  metallic  appearance. 

526.  IRON  DISULPHIDE,  FeS2,  constitutes  the  common  mineral 


318  LESSONS    IN    CHEMISTRY. 

iron  pyrites.  It  is  dimorphous,  being  found  in  cubical  crystals 
of  a  yellow  color  and  metallic  lustre,  known  as  pyrite ;  and  as 
rhombic  prisms  of  a  pale,  greenish-yellow  color,  constituting  mar- 
casite.  When  pyrites  is  heated  in  closed  vessels,  part  of  its  sul- 
phur distils ;  when  it  is  heated  in  contact  with  air,  the  sulphur 
burns  into  sulphur  dioxide,  while  the  iron  remains  as  oxide.  The 
brilliant  metallic  appearance  of  iron  pyrites  has  sometimes  caused 
it  to  be  mistaken  for  gold,  and  it  has  been  called  fool's  gold  :  the 
action  of  heat  at  once  reveals  its  true  character. 

527.  FERRIC    SULPHATE,   Fe2(S04)3.— Ferrous   sulphate,   or 
green  vitriol,  has  already  been  described  (§  123) :  when  crystals 
of  this  salt  are  dissolved  in  water,  and  boiled  with  a  little  less  than 
one-sixth  their  weight  of  sulphuric  acid,  and  small  quantities  of 
nitric  acid  are  added  from  time  to  time,  a  solution  of  ferric  sul- 
phate is  obtained.     When  this  liquid  is  evaporated  to  dryness, 
ferric  sulphate  remains  as  a  yellowish-white  mass,  very  soluble  in 
water.     By  using  a  smaller  quantity  of  sulphuric  acid,  various 
basic  salts  are  obtained,  and  they  may  be  considered  as  ferric  sul- 
phate in  which  one  or  two  groups,  SO4,  are  replaced  by  as  many 
atoms  of  oxygen.     Such  are  Fe20(SO*)2  and  Fe202S04.     A  mix- 
ture  of  these  basic  sulphates  is  employed  in  medicine  under  the 
name  Monsel's  solution.     It  is  astringent  and  styptic,  and  is  valu- 
able for  arresting  hemorrhage. 

528.  TESTS  FOR  IRON. — The  ferrous  and  the  ferric  salts  are 
characterized  by  different  reactions ;  by  reducing  agents  such  as 
nascent  hydrogen  produced  by  zinc  and  hydrochloric  acid,  the  ferric 
salts  are  converted  into  ferrous  salts,  while  ebullition  with  nitric 
acid,  or  the  addition  of  chlorine- water,  will  produce  a  ferric  com- 
pound from  a  ferrous  salt. 

Solutions  of  the  ferrous  salts  are  pale  green  ;  hydrogen  sulphide 
occasions  in  them  no  precipitate,  but  ammonium  sulphide  throws 
down  black  ferrous  sulphide.  The  alkaline  hydroxides  and  ammonia 
produce  greenish-white  precipitates  of  ferrous  hydroxide  which  rap- 
idly become  dark  by  absorbing  oxygen  from  the  air.  Potassium 
ferrocyanide  forms  a  white  precipitate  instantly  changing  to  pale- 
blue  ;  potassium  ferricyanide  a  dark-blue  precipitate,  called  Turn- 
bull's  blue. 


COBALT.  319 

Solutions  of  ferric  salts  are  yellowish-brown  or  brown.  With 
hydrogen  sulphide  they  yield  a  precipitate  of  sulphur,  being 
reduced  to  ferrous  salts  ;  ammonium  sulphide  throws  down  a 
black  precipitate.  The  alkaline  hydroxides  and  ammonia  form  rust- 
colored  precipitates  of  ferric  hydroxide,  insoluble  in  an  excess  of  the 
reagent.  Potassium  ferrocyanide  throws  down  Prussian  blue; 
potassium  ferricyanide  occasions  no  precipitate.  Potassium  sul- 
phocyanate  produces  a  blood-red  color,  due  to  the  formation  of 
ferric  sulphocyanate.  Tannin,  or  an  infusion  of  gall-nuts,  forms 
a  blue-black  and  very  finely  divided  precipitate,  which  long  remains 
suspended  in  the  liquid. 


LESSON    LX. 

COBALT,  NICKEL,  AND    MANGANESE. 

529.  Cobalt,  Co  =  59.— This  metal  is  found  combined  with 
sulphur  and  arsenic ;  smaltite,  CoAs2,  and  cobaltite,  CoAsS,  are 
its  principal  ores.     Much  cobalt  is  also  extracted  from  earthy 
cobalt,  or  asbolite,  a  mixture  or  compound  of  oxide  of  cobalt 
with  hydrated  oxides  of  manganese.     The  metal  is  obtained  by 
reducing  the  oxides  with  carbon  or  hydrogen. 

Pure  cobalt  is  a  grayish- white  metal,  having  a  reddish  tinge 
and  a  strong  lustre.  It  is  malleable  and  ductile.  It  melts  at 
about  1800°,  and  has  a  density  of  8.6.  It  is  attracted  by  the 
magnet.  Neither  dry  nor  moist  air  affect  it  at  ordinary  tem- 
peratures, but  it  is  oxidized  at  a  red  heat. 

Cobalt  forms  cobaltous  oxide,  CoO,  a  sesquioxide,  Co208,  and  several  other 
oxides  which  appear  to  be  formed  by  a  combination  of  these  two  in  different 
proportions.  It  is  in  the  form  of  these  oxides  that  cobalt  is  separated  from 
its  ores. 

530.  COBALT  CHLORIDE,  CoCl2,  is  prepared  by  dissolving  either  the  oxide  or 
carbonate  of  cobalt  in  hydrochloric  acid.     The  solution  is  red,  and,  when  con- 
centrated, deposits  red  crystals  containing  six  molecules  of  water  of  crystalli- 
zation.    Anhydrous  cobalt  chloride  is  blue  :  if  a  little  strong  sulphuric  or 
hydrochloric  acid  be  added  to  a  concentrated  solution  of  cobalt  chloride,  the 


320  LESSONS   IN    CHEMISTRY. 

liquid  becomes  blue.  It  contains  anhydrous  cobalt  chloride.  Writing  made 
on  paper  with  a  very  dilute  solution  of  cobalt  chloride  is  invisible  when  dry  j 
the  small  quantity  of  the  salt  present  is  hydrated  ;  but  if  the  paper  be  heated, 
the  characters  become  blue,  for  the  water  is  driven  off.  After  exposure  to  the 
air  for  a  time,  the  characters  again  fade,  the  cobalt  chloride  absorbing  atmos- 
pheric moisture.  The  solution  is  employed  as  a  sympathetic  ink. 

531.  COBALT  BLUE. — The  ores  of  cobalt  are  principally  em- 
ployed for  the  manufacture  of  a  dark-blue  substance  generally 
called  smalt.  This  is  a  mixture  of  cobalt  silicate  and  potassium 
silicate.  It  is  prepared  by  partially  roasting  the  ore  in  order  to 
convert  the  greater  part  of  the  cobalt  into  oxide.  The  roasted 
mass  is  then  pulverized  and  melted  with  a  mixture  of  potassium 
carbonate  and  white  quartz  sand.  A  blue,  vitreous  mass  is  thus 
obtained,  which  floats  on  a  fused  mass  containing  the  iron,  nickel, 
copper,  and  unaltered  sulphur  and  arsenic  of  the  ore.  This  mix- 
ture has  a  metallic  appearance  ;  it  is  called  speiss,  and  is  used  for 
the  preparation  of  nickel.  While  still  molten,  the  blue  glass  con- 
stituting smalt  is  poured  into  water,  in  which  it  breaks  up  into 
small  fragments,  which  are  readily  pulverized. 

532.  TESTS  FOR  COBALT. — The  more  ordinary  salts  of  cobalt  form  rose- 
colored  or  currant-red  solutions,  but  if  these  solutions  contain  free  acid,  they 
become  blue  when  heated.  They  are  not  precipitated  by  hydrogen  sulphide 
in  acid  liquids,  but  in  neutral  solutions  black  CoS  is  thrown  down  ;  ammonium 
sulphide  forms  a  black  precipitate.  The  alkaline  hydroxides  produce  blue  pre- 
cipitates, which  by  boiling  are  converted  into  rose-colored  cobaltous  hydroxide, 
Co(OH)2.  Ammonia-water  occasions  a  blue  precipitate,  which  dissolves  in  an 
excess  of  the  reagent,  an  ammonio-cobalt  salt  being  formed.  When  strongly 
heated  with  a  little  borax  on  the  end  of  a  platinum  wire,  the  compounds  of 
cobalt  yield  beads  of  a  blue  glass. 

533.  Nickel,  Ni  —  59. — Nickel  is  found  as  arsenide  in  nicco- 
lite  or  kupfcr  nickel,  NiAs,  as  sulpharsenide  in  gersdorffite,  NiAsS, 
as  sulphide  in  millerite,  NiS,  and  in  nickeliferous  pyrites,  and 
as  a  hydrated  silicate  in  garnierite.  The  metal  is  extracted 
by  various  processes  from  these  minerals  and  from  the  speiss 
formed  during  the  manufacture  of  smalt. 

Pyrites,  containing  small  proportions  of  nickel  and  copper,  are  treated  as 
described  under  Copper  (see  p.  284),  and  so  converted  into  a  matte  in  which 
the  two  metals  are  concentrated,  while  most  of  the  iron  passes  into  the  slag. 
Arsenical  ores  and  speiss  are  first  oxidized  by  roasting  and  then  fused  (smelted) 
with  sand  and  soda.  The  products  are  a  speiss,  consisting  of  the  arsenides  of 
nickel,  cobalt,  and  copper,  and  a  slag  which  contains  the  iron  and  some  of  the 


NICKEL.  321 

cobalt  in  the  form  of  silicates  and  arsenates.  The  whole  process  is  then  re- 
peated with  the  speiss  to  increase  the  proportion  of  nickel. 

The  separation  of  nickel  from  matte  and  speiss  is  effected  by  either  a  dry 
process  or  a  wet  process.  In  the  former  sulphur  and  arsenic  are  removed  by 
roasting,  and  fusion  with  soda  and  saltpetre,  nickel  oxide  remaining  after 
lixiviating  the  fused  mass  with  water.  A  better  way  is  to  roast  to  thorough 
oxidation,  and  to  dissolve  the-  resulting  oxides  in  sulphuric  acid.  From  the 
solution  the  copper  is  removed  by  means  of  hydrogen  sulphide ;  the  iron  is  con- 
verted into  the  ferric  state  and  precipitated  by  calcium  carbonate,  and  cobalt 
thrown  down  as  sesquioxide  by  adding  bleaching  powder  to  the  neutral  solution. 
Upon  addition  of  milk  of  lime  to  the  decanted  liquid,  the  nickel  is  obtained 
as  the  hydroxide,  Ni(OH)2,  which,  by  ignition,  is  converted  into  the'oxide. 

The  oxide,  after  being  purified,  is  reduced  by  mixing  it  with  charcoal  and 
heating  the  mixture  to  a  high  temperature.  The  resulting  metal  always  con- 
tains carbon  and  small  amounts  of  metallic  impurities. 

Pure  nickel  may  be  obtained  by  strongly  heating  the  oxalate 
out  of  contact  with  the  air,  by  reducing  the  pure  oxide  by 
hydrogen,  by  electrolyzing  solutions  of  nickel  salts,  and  by  de- 
composing nickel  carbonyl,  Ni(CO)4  (see  p.  153),  by  heat. 

Nickel  is  a  silver-white  metal,  capable  of  taking  a  high  polish. 
It  is  malleable,  ductile,  and  very  tenacious.  Its  density  is  about  8.5. 
It  is  attracted  by  the  magnet.  It  is  the  hardest  of  the  more  common 
metals.  It  is  not  affected  by  the  air  at  ordinary  temperatures,  but 
becomes  oxidized  at  a  red  heat.  It  is  slowly  dissolved  by  dilute 
hydrochloric  and  sulphuric  acids,  more  rapidly  by  nitric  acid. 

Nickel  is  employed  in  the  manufacture  of  a  number  of  alloys. 
German  silver  contains  25  per  cent,  of  nickel,  25  per  cent,  of 
zinc,  and  50  per  cent,  of  copper,  but  the  proportions  vary 
greatly.  The  white  nickel  coins  of  the  United  States  contain 
25  per  cent,  of  nickel  and  75  per  cent,  of  copper.  Nickel-steel, 
an  alloy  of  nickel  and  iron,  is  extensively  used  for  armor-plates, 
and  in  the  construction  of  heavy  machinery. 

Nickel  is  largely  employed  for  plating  articles  of  brass,  iron, 
and  steel,  and  its  hardness,  its  high  lustre,  and  its  freedom  from 
rust  render  it  admirably  adapted  to  this  purpose.  The  well- 
cleaned  objects  are  attached  to  the  zinc  pole  of  a  voltaic  battery 
and  immersed  in  a  solution  of  nickel  and  ammonium  double 
sulphate :  the  positive  pole  of  the  battery  is  connected  with  a 
plate  of  pure  nickel  dipped  in  the  same  liquid. 

21 


322  LESSONS   IN   CHEMISTRY. 

534.  NICKEL  CHLORIDE,  NiCl2,  is  made  by  dissolving  the  oxide  or  hydrate 
in  hydrochloric  acid.     When   sufficiently  concentrated,  the  green  solution 
deposits  green  crystals  containing  NiCl2  +  6H20. 

535.  NICKEL  MONOXIDE,  NiO,  is  a  green  powder,  obtained  by  strongly  heat- 
ing the  carbonate  or  nitrate.     Nickel  hydroxide,  Ni(OH)2,  is  thrown  down 
as  a  pale-green  precipitate  when  an  alkaline  hydrate  is  added  to  the  solution 
of  a  nickel  salt.     When  chlorine  is  passed  through  water  in  which  this  pre- 
cipitate is  suspended,  a  hydrate  of  nickel  sesquioxide,  Ni203,  is  formed. 

536.  NICKEL  SULPHATE,  NiSO*. — When  nickel  oxide  or  hydroxide  is  dissolved 
in  dilute  sulphuric  acid,  and  the  solution  is  allowed  to  evaporate  spontaneously, 
green  crystals  of  the  sulphate  with  seven  molecules  of  water  of  crystallization 
are  deposited.      With  ammonium  sulphate,  this  compound  forms  a  double  salt 
in  fine  bluish-green  crystals  containing  NiS04.(NH*)2SO*  +  6H20.     This  is 
the  salt  used  in  nickel-plating. 

537.  TESTS  FOR  NICKEL. — The  anhydrous  nickel  salts  are  yellow,  but  the 
crystallized  salts  and  their  solutions  are  emerald-green.     If  the  solution  be 
acid,  hydrogen  sulphide  produces  no  precipitate,  but  a  black  precipitate  of 
sulphide  is  thrown  down  if  the  solution  contain  sodium  acetate.     The  same 
precipitate  is  formed  by  ammonium  sulphide.     The  alkaline  hydroxides  and 
carbonates  occasion  pale-green  precipitates.     Ammonia-water  forms  a  green 
precipitate,  which  dissolves  in  an  excess  of  the  reagent,  yielding  a  blue  solution. 

538  MANGANESE,  Mn  =  55. — This  metal  has  been  obtained 
by  reducing  the  oxides  with  either  carbon  or  aluminium  at  high 
temperatures.  Its  properties  are  greatly  modified  by  small  pro- 
portions of  impurities.  Pure  manganese  appears  to  be  soft  and 
malleable ;  the  presence  of  carbon  renders  it  hard  and  brittle. 
The  metal  has  a  steel-gray  color ;  it  melts  and  volatilizes  in  the 
electric  arc.  It  is  attacked  by  moist  air,  especially  when  it 
contains  carbon.  Three  of  its  oxides  are  found  native  in  the 
minerals  braunite,  Mn203,  pyrolusite,  MnO2,  and  hausmannite, 
Mns04. 

539.  MANGANESE  DIOXIDE,  MnO2,  is  commonly  called  black 
oxide  of  manganese.  When  it  is  heated  to  redness,  it  loses  oxy- 
gen, and  is  converted  into  red  manganeso-manganic  oxide,  Mn30*. 

3Mn02         =         Mn3Q*         +         O2 

Oxygen  is  also  evolved,  while  manganous   sulphate  is  formed, 
when  the  dioxide  is  heated  with  sulphuric  acid. 

2MnO*        +        2H2SO*        =        2MnSO*        +        2H'0         +        0» 

When  heated  with  hydrochloric  acid,  manganese  dioxide  yields 
manganese  chloride,  water,  and  chlorine :  large  quantities  of  the 


MANGANIC   ACID.  323 

dioxide  are  used  for  the  manufacture  of  chlorine,  and  in  the 
solution  of  manganese  chloride  the  dioxide  is  regenerated.  The 
process  consists  in  mixing  the  liquid  with  milk  of  lime,  by  which 
calcium  chloride  and  manganous  hydroxide,  Mn(OH)2,  are 
formed  :  heated  air  is  then  blown  through  the  mixture,  and  the 
manganous  hydroxide  is  converted  into  the  dioxide,  from  which 
the  solution  of  calcium  chloride  is  decanted. 

Manganese  dioxide  is  also  employed  to  decolorize  glass  ren- 
dered dark  by  carbonaceous  matter  or  green  by  iron.  In  the 
first  case  it  oxidizes  the  carbon,  and  in  the  second  it  converts 
the  ferrous  into  ferric  silicate,  of  which  the  yellow  tint  is  neu- 
tralized by  the  purple  color  of  manganic  silicate. 

540.  MANGANIC  ACID,  H2Mn04. — When  strongly  heated  with 
alkaline  hydroxides,  manganese  dioxide  absorbs  oxygen  from  the  air, 
and  an  alkaline  manganate  is  formed.     A  mixture  of  manganese 
dioxide  and  potassium  hydroxide  may  be  fused  in  a  silver  or  iron 
dish,  and,  when  the  cold  mass  is  treated  with  water,  a  green  solu- 
tion is  obtained.     If  this  be  evaporated  at  a  low  temperature  in  a 
vacuum,  it  deposits  green  crystals  of  potassium  manganate. 

When  the  alkaline  manganates  are  heated  to  450°  in  a  current 
of  steam,  they  are  decomposed  into  alkaline  hydroxide  and  manga- 
nese dioxide.  This  decomposition  has  been  applied  to  the  manu- 
facture of  oxygen  on  a  large  scale.  A  mixture  of  sodium  hydroxide 
and  manganese  dioxide  is  heated  in  a  current  of  air ;  oxygen  is 
absorbed,  and  sodium  manganate  is  formed. 

MnQ2         +         2NaOH         +         0         =         Na'MnO*         +         IPO 
Manganese  dioxide.  Sodium  manganate. 

The  air  is  then  stopped,  and  steam  is  passed  over  the  heated 

manganate,  reproducing  sodium  hydroxide  and  manganese  dioxide, 

while  oxygen  is  disengaged. 

Na'MnO*        +        R2Q        =        2NaOH        +        MnO*        +        0 
The  oxygen,  with   the   excess  of  steam,  is  led  through  cold 

pipes,  where  the  steam  is  condensed,  while  the  oxygen  passes  on 

to  appropriate  gas-holders. 

541.  PERMANGANATES. — When  the  green  solution  of  potas- 
sium  manganate  is  boiled,  its  color  changes  to  red,  while  hydrated 


324  LESSONS    IN    CHEMISTRY. 

manganese  dioxide  separates  in  brown  flakes.  The  red  color  is 
due  to  the  formation  of  potassium  permanganate,  and  the  solu- 
tion contains  free  potassium  hydroxide. 

3K*MnO*       +    2H2Q     =  2KMnO*  +      MnO2     +     4KOH 

Potassium  manganate.  Potassium  permanganate. 

A  similar  reaction  takes  place  when  an  acid  is  added  to  the 
solution  of  a  manganate. 

Potassium  permanganate  is  made  by  heating  in  an  iron  crucible 
a  mixture  of  five  parts  of  potassium  hydroxide  with  a  little  water, 
and  three  and  a  half  parts  of  potassium  chlorate  with  four  of 
manganese  dioxide  in  fine  powder.  The  temperature  is  gradually 
raised  to  dull  redness,  the  mass  being  constantly  stirred.  It  is 
allowed  to  cool,  and,  after  being  pulverized,  is  thrown  into  two 
hundred  parts  of  boiling  water,  and  stirred  until  the  liquid  has 
assumed  a  purple  color.  It  is  then  left  to  settle ;  the  clear  liquid 
is  decanted,  neutralized  with  nitric  acid,  and  evaporated  on  a 
water-bath.  The  crystals  which  separate  on  cooling  are  drained 
on  a  clean  brick. 

They  are  purple-black  needles,  having  a  metallic  reflection, 
soluble  in  about  fifteen  times  their  weight  of  cold  water.  The 
solution  has  an  intense  purple  color.  Potassium  permanganate  is 
an  energetic  oxidizing  agent ;  its  solution  is  at  once  decolorized  by 
sulphur  dioxide,  which  it  converts  into  sulphuric  acid,  and  the 
liquid  contains  sulphuric  acid,  potassium  sulphate,  and  manganous 
sulphate. 

2KMnO<     +     5SQ2     +     2R2Q    =     K'SO*     +  2MnSO*     +     2R2SO* 
Potassium  permanganate.  Manganous  sulphate. 

The  oxidizing  properties  of  potassium  permanganate  are  largely 
employed  in  the  laboratory. 

542.  TESTS  FOR  MANGANESE. — The  salts  of  manganese  are 
colorless  or  pale  rose-colored.  They  are  not  precipitated  by  hydro- 
gen sulphide,  but  ammonium  sulphide  throws  down  flesh -colored 
manganese  sulphide.  The  alkaline  hydroxides  produce  dirty- white 
precipitates  of  manganese  hydroxide,  which  soon  absorbs  oxygen 
from  the  air  and  becomes  brown.  When  heated  with  a  little 
potassium  hydroxide  or  nitrate  or  sodium  carbonate  on  a  piece  of 


CHROMIUM.  325 

platinum  foil,  they  yield  a  bluish-green  mass  of  an  alkaline 
manganate,  which  forms  a  red  solution  when  treated  with  a  little 
dilute  nitric  acid. 


LESSON   LXI. 

CHROMIUM  AND   TIN. 

543.  Chromium,  Cr  =  52.5. — Chromium  exists  in  the  min- 
eral chromite,  or  chrome  iron,  which  is  a  compound  of 'chromium 
oxide  and  ferrous  oxide,  and  may  be  considered  as  ferroso-ferric 
oxide  in  which  the  ferric  oxide  is  replaced  by  the  sesquioxide 
of  chromium,  FeO.Cr203.  It  is  found  also  in  the  mineral  cro- 
coite,  PbCrO*.  The  metal  is  obtained  by  reducing  the  oxide 
either  by  means  of  carbon  in  the  electric  furnace,  or  by  heating 
it  with  aluminium.  Chromium  is  a  grayish-white,  very  brilliant 
metal,  having  a  density  of  6.92.  It  is  rather  soft,  but  a  small 
proportion  of  carbon  renders  it  exceedingly  hard.  The  pure 
metal  is  not  magnetic,  and  very  difficult  to  fuse. 

544.  CHROMIC  CHLORIDE,  CrCl3,  is  obtained  by  passing  chlorine  gas  over 
an  incandescent  mixture  of  chromium  sesquioxide  and  charcoal ;  it  then  sub- 
limes and  condenses  in  brilliant  violet  scales  in  the  cooler  parts  of  the  tube. 
By  the  action  of  hydrogen  at  a  red  heat,  it  is  converted  into  white  chromoua 
chloride,  CrCl2.     Chromic  chloride  is  insoluble  in  water,  but  dissolves  readily 
in  presence  of  a  small  quantity  of  chromous  chloride,  yielding  a  green  solution 
from  which  there  may  be  obtained  a  crystallized  hydrate,  CrCl3  +  6H20. 

545.  CHROMIUM  SESQUIOXIDE,  Cr203. — When  potassium  dichromate  is  heated 
in  a  crucible  with  about  half  its  weight  of  sulphur,  a  mass  is  obtained  from 
which  water  dissolves  potassium  sulphate,  leaving  chromium  sesquioxide  as  a 
green  powder.     Instead  of  sulphur,  starch  in  quantity  equal  to  one-fourth 
the  weight  of  the  dichromate  may  be  employed,  but  the  resulting  oxide  must 
afterwards  be  recalcined  in  the  air,  to  burn  out  traces  of  carbon.     It  is  in  the 
latter  manner  that  the  fine  chrome  green  used  for  painting  on  porcelain  is  ob- 
tained.    Chromium  sesquioxide  is  not  decomposed  by  heat,  and  fuses  only  at 
very  elevated  temperatures.     A  corresponding  hydroxide,  Cr(OH)3,  is  thrown 
down  as  a  bluish-green  precipitate  when  ammonia-water  is  added  to  the  green 
solution  of  chromic  chloride.    The  same  hydroxide  is  precipitated  by  the  alka- 
line hydroxides,  but  dissolves  in  an  excess  of  the  reagent ;  when  the  liquid 
is  boiled,  an  insoluble  hydroxide  is  thrown  down. 

546.  CHROMIC  ANHYDRIDE,  CrO3. — This  compound  is  com- 
monly called  chromic  acid.  It  is  prepared  by  mixing  a  cold  satu- 


326  LESSONS    IN    CHEMISTRY. 

rated  solution  of  potassium  dichromate  with  one  and  a  half  times 
its  volume  of  strong  sulphuric  acid.  As  the  liquid  cools,  chro- 
mium anhydride  separates  in  crimson  needles,  which  are  quickly 
drained  on  a  dry  brick  and  recrystallized  in  the  smallest  possible 
quantity  of  warm  water.  It  is  a  deliquescent  substance,  exceed- 
ingly soluble  in  water,  and  the  solution  has  an  orange  color.  It 
energetically  oxidizes  many  bodies.  With  hydrochloric  acid  it 
forms  water  and  chromic  chloride,  while  chlorine  is  set  free. 

2Cr03     +     12HC1    =     2CrCl3     +     6H20     +     3C12 
It  instantly  oxidizes  sulphur  dioxide,  chromium  sulphate  being 

formed. 

2Cr03         +         3S02        =         Cr2(S04)3 

It  oxidizes  alcohol  and  ether  with  such  energy  that  those  com- 
pounds are  inflamed. 

547.  CHROMATES. — The  solution  of  chromium  anhydride  must 
be  regarded  as  containing  chromic  acid,  H2O04  =  H20  -j-  CrO3, 
corresponding  in  molecular  constitution  to  sulphuric  acid.     The 
chromium  compounds  are  all  derived  from  potassium  dichromate, 
which  is  manufactured  from  chrome  iron.     A  mixture  of  the 
pulverized  mineral  with  potash  and  lime  is  roasted  with  full 
access  of  air :  calcium  and  potassium  chromates  are  produced, 
oxygen  being  absorbed.    The  mass  is  extracted  with  a  hot  solution 
of  potassium  sulphate,  which   converts  the  calcium  chromate 
into  the  potassium  salt.     The  decanted  yellow  liquid  is  then 
mixed  with  enough  sulphuric  acid  to  form  the  dichromate. 

2K2CrO*    +     H2SO*    =     K*CW     +     K*SO*     +     H20 
This  compound,  being  less  soluble  than  the  neutral  chromate, 
crystallizes  as  the  solution  cools. 

548.  Potassium  chromate,  K2Cr04,  forms  beautiful,  lemon-yel- 
low, anhydrous  crystals,  which  are  very  soluble  in  water,  to  which 
they  impart  an  intense  yellow  color. 

549.  Potassium  dichromate,  K2Cr20T,  forms  large,  orange-red 
crystals,  soluble  in  about  eight  times  their  weight  of  cold  water, 
and  in  much  less  boiling  water.     By  heat  they  are  decomposed 
into  potassium  chromate,  chromium  oxide,  and  oxygen. 

2K2Cr207         =         2K2CrO*         +         Cr203         +         0s 


CHROMIUM.  327 

Potassium  dichromate  is  an  energetic  oxidizing  agent.  When 
heated  with  sulphuric  acid,  it  yields  oxygen,  while  chrome  alum 
will  crystallize  from  the  liquid  obtained  by  treating  the  residue 
with  boiling  water. 

R2Cr207     +     4H2SO*    =     Cr2(SO*)3.K2SO*     +    4H2Q     +     O3 

When  sulphur  dioxide  is  passed  into  a  solution  of  potassium 
dichromate,  the  orange  color  is  gradually  replaced  by  green  :  while 
the  sulphur  dioxide  becomes  sulphuric  acid,  both  chromium  and 
potassium  are  converted  rnto  sulphates,  and  the  liquid  will  yield 
chrome  alum  if  sulphuric  acid  be  added. 

K2Cr207     +     3S02     +     H2SO*    =     Cr2(S04)3.K2SO*     +     H20 

550.  Ammonium  dichromate,  (NH4)2Cr*07,  may  be  made  by  dividing  a  solu- 
tion of  chromic  acid  into  two  equal  portions,  neutralizing  one  with  ammonia- 
water,  and  then  adding  the  other.     When  the  solution  is  evaporated,  the  am- 
monium dichromate  separates  in  red  crystals,  which,  when  heated,  yield  pure 
chromium  trioxide  in  a  curious  pulverulent  form,  resembling  green  tea. 

(NH*)2Cr207     =     Cr203     +     4H20     +     N2 

551.  Lead  chromate,  PbCrO4,  occurs  in  the  mineral  crocoite,  and  is  made 
by  mixing  solutions  of  potassium  chromate  and  lead  acetate;  potassium  ace- 
tate remains  in  solution,  while  the  lead  chromate  forms  a  dense  yellow  pre- 
cipitate, which   when   washed  and  dried   constitutes  chrome   yellow.     It  is 
insoluble  in  water  and  in  acetic  acid,  but  dissolves  in  solutions  of  the  alkaline 
hydroxides.     It  melts  at  a  red  heat,  and  is  readily  reduced  by  both  hydrogen 
and  charcoal.     It  is  sometimes  substituted  for  cupric  oxide  in  the  analysis  of 
carbon  compounds. 

552.  TESTS  FOR  CHROMIUM. — Although  there  is  a  series  of 
chromous   salts  in  which  the  chromium   atom  is  diatomic,  the 
reactions  of  the  salts  corresponding  to  the  sesquioxide  are  suffi- 
cient to  characterize  this  element.    In  the  green  solutions  of  these 
compounds  hydrogen  sulphide  produces  no  precipitate  :  ammonium 
sulphide   throws  down  chromium  hydroxide,  hydrogen  sulphide 
being  disengaged. 

2CrCl3  +  3(NH4)2S  +  6H20  =  2Cr(OH)3  +  6NH4C1  +  3H2S 
The  alkaline  hydroxides  and  ammonia  produce  the  same  green  pre- 
cipitate, which  dissolves  readily  in  an  excess  of  the  former  re- 
agents, more  slowly  in  ammonia-water.  When  the  solution  so 
obtained  is  boiled,  anhydrous  chromium  sesquioxide  is  precipitated, 
and  does  not  redissolve  on  cooling. 


328 


LESSONS   IN   CHEMISTRY. 


The  chromates  may  be  identified  by  heating  them  in  a  test- 
tube  with  a  little  common  salt  and  sulphuric  acid.  Irritating 
red  vapors  of  chromyl  chloride,  Cr02CP,  are  disengaged,  and  if 
conducted  into  a  cold  tube  will  condense  to  a  blood-red  liquid. 
When  passed  into  water,  these  vapors  are  decomposed  into 
hydrochloric  and  chromic  acids. 

Cr02Cl2     +     H20     =     CrO3     +     2HC1 

In  neutral  solutions  of  chromates,  barium  chloride  and  lead 
acetate  produce  yellow  precipitates,  and  silver  nitrate  throws 
down  a  red  compound. 

553.  Closely  related  to  chromium  in  their  chemical  relations  are  the  elements 
molybdenum,  tungsten,  and  uranium.  Molybdenum  occurs  chiefly  as  the  sul- 
phide, MoS2,  in  the  mineral  molybdenite.  Tungsten  is  found  in  various  tung- 
states,  as  in  the  mineral  wolfram,  which  is  a  tungstate  of  iron  and  manganese. 
The  principal  uranium  mineral  is  pitchblende,  an  impure  oxide  of  uranium  of 
varying  color.  It  was  in  a  variety  of  this  mineral  that  helium  was  discovered. 
The  three  metals  have  been  recently  produced  in  considerable  quantities  and 
in  a  very  pure  state  by  means  of  the  electric  furnace.  They  resemble  chro- 
mium in  their  properties  :  they  form  trioxides,  which,  like  chromium  triox- 

ide,  are  the  anhyrides  of  corresponding 
acids.  A  number  of  lower  oxides  are 
also  known. 

554.  Tin,  Sn  =  118.— Tin  is 
rarely  found  in  the  metallic  state 
in  nature :  its  only  workable  ore 
is  the  dioxide,  which  constitutes 
the  mineral  cassiterite.  The 
principal  tin-mines  are  in  Corn- 
wall, England,  and  in  various 
parts  of  Farther  India  and 
Australia. 

The  ore  is  crushed,  and  the  dioxide, 
being   very   heavy,  can    be   separated 
FlG.  124.  from  the  lighter  earthy  matters  by  wash- 

ing in  a  stream  of  water.     It  is  then 

roasted,  the  sulphides  and  arsenides  of  iron  and  copper  present  being  converted 
into  oxides,  which  are  removed  by  a  second  washing.  The  purified  cassiterite 
is  mixed  with  charcoal  and  fed  into  a  cupola  furnace  (Fig.  124),  where  the 
combustion  is  supported  by  a  blast  of  air.  The  reduced  tin  collects  on  the 
hearth  of  the  furnace,  and  runs  into  a  basin,  where  it  is  stirred  with  poles  of 


TIN.  329 

green  wood.  The  gases  given  off  reduce  any  oxide  that  has  been  formed,  and 
bring  to  the  surface  of  the  molten  metal  the  foreign  matters,  which  form  a 
dross.  The  tin  is  further  purified  by  being  melted  at  a  low  temperature  on  the 
inclined  hearth  of  a  reverberatory  furnace.  Being  more  fusible  than  the  foreign 
metals  present,  it  runs  into  a  cavity  prepared  for  it,  while  the  less  fusible 
metals  remain  on  the  hearth. 

Tin  is  a  silvery-white  metal,  having  a  density  of  about  7.3.  It 
melts  at  228°,  and  may  be  crystallized  by  slow  cooling.  It  is 
malleable  and  ductile :  when  a  bar  of  tin  is  bent,  it  produces  a 
peculiar  noise,  called  the  cry  of  tin,  caused  by  the  sliding  of  the 
crystals  over  one  another. 

It  is  not  affected  by  the  air  at  ordinary  temperatures,  but  when 
melted  absorbs  oxygen,  and  by  stirring  may  be  entirely  converted 
into  the  dioxide.  It  is  dissolved  by  hydrochloric  acid,  hydrogen 
being  disengaged,  while  stannous  chloride  is  formed.  Nitric  acid 
converts  tin  into  dioxide,  giving  off  torrents  of  red  vapors.  Hot 
solutions  of  the  alkaline  hydroxides  dissolve  tin,  forming  alkaline 
stannates,  and  disengaging  hydrogen. 

Tin  is  used  for  the  manufacture  of  tin  foil,  employed  for 
enveloping  tobacco,  chocolate,  etc. ;  also  for  tinning  copper  and 
iron,  which  is  accomplished  by  dipping  the  perfectly  clean  objects 
into  a  bath  of  molten  tin.  Its  resistance  to  the  action  of  vegetable 
acids  renders  it  invaluable  as  a  coating  for  culinary  utensils.  It 
enters  into  the  composition  of  plumbers'  solder,  which  is  an  alloy 
of  tin  and  lead.  Bronze,  bell-metal,  gun-metal,  and  speculum- 
metal  are  alloys  of  tin  and  copper  (page  287).  Britannia  metal 
is  tin  alloyed  with  a  small  proportion  of  antimony,  bismuth,  and 
copper. 

In  its  compounds  tin  is  either  diatomic  or  tetratomic.  Those 
in  which  it  is  diatomic  are  called  stannous  compounds,  while  in 
the  stannic  compounds  it  is  tetratomic,  one  atom  of  tin  having  the 
same  combining  power  as  four  atoms  of  hydrogen. 

555.  STANNOUS  CHLORIDE,  SnCl2. — Anhydrous  stannous  chlo- 
ride is  obtained  by  passing  hydrochloric  acid  gas  over  heated  tin. 
It  is  a  white  solid,  fusible  at  250°.  When  it  is  dissolved  in  a 
small  quantity  of  water,  or  when  metallic  tin  is  dissolved  in  hot 
hydrochloric  acid,  a  solution  is  obtained  which  when  sufficiently 
concentrated  deposits  crystals  of  a  hydrate  containing  SnCl2  -f- 


330  LESSONS    IN   CHEMISTRY. 

2H20.  These  crystals  are  known  in  commerce  as  tin  salt  or  tin 
crystals.  They  are  soluble  in  a  small  quantity  of  water,  but  when 
the  solution  is  diluted,  a  deposit  of  an  oxychloride  is  formed  con- 
taining SnCP.SnO.  At  the  same  time  a  certain  proportion  of 
the  stannous  chloride  is  converted  into  stannic  chloride,  SnCl*. 
This  decomposition  is  prevented  by  the  presence  of  free  hydro- 
chloric acid,  or  by  a  small  quantity  of  ammonium  chloride.  Stan- 
nous  chloride  is  a  reducing  agent:  a  few  drops  of  its  solution 
instantly  decolorize  the  purple  solution  of  potassium  permanga- 
nate ;  it  reduces  the  salts  of  silver  and  gold,  setting  free  the  metal. 
When  it  is  added  to  a  solution  of  mercuric  chloride,  a  white  pre- 
cipitate of  mercurous  chloride  is  formed,  which  an  excess  of 
stannous  chloride  converts  into  a  gray  deposit  of  finely-divided 
metallic  mercury.  In  these  reactions  the  stannous  chloride  be- 
comes stannic  chloride.  Stannous  chloride  is  used  as  a  mordant 
in  dyeing. 

556.  STANNIC  CHLORIDE,  SnCl*,  is  formed  with  the  production  of  light  and 
heat  by  the  direct  union  of  tin  and  chlorine.     It  is  prepared  by  passing  dry 
chlorine  over  melted  tin  contained  in  a  retort ;  it  then  distils,  and  condenses 
as  a  heavy,  fuming,  yellow  liquid,  which  boils  at  120°.     It  combines  energeti- 
cally with  water,  forming  crystals  of  a  hydrate  containing  SnCl*  +  5H20.    The 
same  hydrate  may  be  made  by  dissolving  tin  in  hydrochloric  acid  and  from 
time  to  time  adding  small  quantities  of  nitric  acid.     The  crystals  are  soluble 
in  water,  yielding  a  limpid  solution. 

557.  STANNIC  OXIDE,  SnO2. — When  an  alkaline  hydroxide  is  added  to  a  solu- 
tion of  stannous  chloride,  stannous  hydrate  is  formed  as  a  white  precipitate, 
which,  by  boiling,  is  converted  into  black  stannous  oxide,  SnO.     The  addition 
of  ammonia  to  a  solution  of  stannic  chloride  throws  down  a  white  gelati- 
nous precipitate  of  stannic  hydrate,  H2Sn03,  which  by  the   action  of  heat  is 
converted  into  stannic  oxide,  SnO2.     This  compound  is  found  in  nature  in 
hard,  transparent  crystals ;  it  is  cassiterite.     It  is  an  acid  oxide,  and  stannic 
hydrate  reacts  with  the  bases,  forming  stannates  whose  compositions  corre- 
spond to  the  carbonates.     The  white  powder  produced  by  the  action  of  nitric 
acid  on  tin  is  a  stannic  hydrate,  containing  Sn(OH)4  ==  SnO2  +  2H20. 

558.  Sulphides  of  Tin. — By  heating  together  the  proper  proportions  of  tin 
and  sulphur,  two  sulphides  may  be  obtained.     Stannous  sulphide,  SnS,  is  a 
gray,  crystalline  mass.     The  preparation  of  stannic  sulphide,  SnS2,  requires 
particular  precautions ;  an  amalgam  of  tin  with  half  its  weight  of  mercury 
is  mixed  with  flowers  of  sulphur  and  ammonium  chloride  and  heated  to  dull 
redness.     Mercuric  sulphide,  ammonium  chloride,  and  the  excess  of  sulphur 
sublime,  while  the  interior  of  the  vessel  becomes  lined  with  a  golden-yellow, 


PLATINUM    AND    ITS   ALLIED    METALS.  331 

crystalline  mass  of  stannic  sulphide.  The  operation  must  then  be  arrested, 
or  this  compound  will  be  decomposed  into  stannous  sulphide  and  sulphur;  the 
addition  of  the  mercury  and  ammonium  chloride  is  intended  to  keep  the  tem- 
perature down  to  the  volatilizing  points  of  mercuric  sulphide  and  ammonium 
chloride.  Stannic  sulphide  forms  soft,  crystalline  scales,  called  mosaic  gold. 

559.  TESTS  FOR  TIN. — In  stannous  solutions,  both  hydrogen 
sulphide  and  ammonium  sulphide  form  brown  precipitates,  soluble 
in  yellow  ammonium  sulphide  (§  143).     The  alkaline  hydroxides 
and  ammonia  give  white  precipitates,  soluble  in  an  excess  of  the 
former  reagents,  but  insoluble  in  ammonia.     Gold  trichloride  throws 
down  purple  of  Cassius.     In  mercuric  chloride  solutions,  an  excess 
of  stannous  chloride  precipitates  gray  metallic  mercury. 

In  stannic  solutions,  hydrogen  sulphide  and  ammonium  sulphide 
form  yellow  precipitates,  soluble  in  a  large  quantity  of  the  latter 
reagent.  Apiece  of  zinc  placed  in  either  a  stannous  or  a  stannic 
solution  becomes  covered  with  a  deposit  of  tin,  which  may  be 
rendered  brilliant  by  burnishing. 

560.  The  elements  titanium,  zirconium,  and  thorium  closely  resemble  tin  in 
their  chemical  relations,  although  their  physical  properties  are  very  different. 
Each  forms  a  tetrachloride  and  a  dioxide.     Titanium  occurs  as  dioxide  in  the 
minerals  rutile,  anatase,  and  brookite.     Zirconium  exists  as  a  silicate  in  zircon, 
and  thorium  is  a  constituent  of  a  number  of  minerals,  such  as  monazite  and 
thorite.     The  oxides  of  thorium  and  zirconium  have  found  an  application  in 
the  "  Welsbach"  burner,  in  which  a  gauze  of  these  compounds  is  rendered 
incandescent  by  a  non-luminous  gas  flame. 

The  very  rare  element  germanium  also  belongs  to  this  group. 


LESSON    LXII. 
PLATINUM  AND   ITS  ALLIED   METALS. 

561.  Like  gold,  platinum  is  found  in  the  metallic  state  in 
rounded  granules  distributed  through  sandy  deposits.  Being 
very  heavy,  it  is  also  separated  like  gold,  by  washing  the  sand  in 
a  stream  of  water.  The  native  platinum,  however,  is  not  pure  : 
besides  containing  traces  of  gold,  copper,  and  iron,  it  is  alloyed 
with  several  other  metals  which  it  resembles  in  certain  properties, 
and  which  are  called  the  platinum  metals.  They  are  rhodium, 


332  LESSONS   IN    CHEMISTRY. 

ruthenium,  palladium,  iridium,  and  osmium.  The  platinum  is  ex- 
tracted by  treating  the  grains  first  with  dilute  nitre-hydrochloric 
acid,  which  removes  all  excepting  the  platinum  metals,  and  then 
heating  it  with  strong  nitro-hydrochloric  acid,  which  dissolves  the 
platinum,  leaving  osmium  and  the  greater  part  of  the  iridium. 
The  liquid  is  then  exactly  neutralized  with  sodium  carbonate,  and 
a  solution  of  mercuric  cyanide  is  added.  This  throws  down  a 
precipitate  of  palladium  cyanide,  which  is  removed  by  filtration, 
and  the  clear  liquid  is  treated  with  ammonium  chloride.  A  crys- 
talline precipitate  of  a  double  chloride  of  platinum  and  am- 
monium forms,  and  this,  when  calcined,  leaves  a  porous  gray 
residue  of  platinum  sponge.  Platinum  so  prepared  always  con- 
tains some  iridium,  for  the  latter  metal  also  separates  as  a  double 
chloride  when  the  ammonium  chloride  is  added. 

In  order  to  agglomerate  the  spongy  platinum,  it  is  made  into 
a  stiff  paste  with  a  little  water,  and  this  is  strongly  compressed 
in  a  slightly  conical  steel  cylinder.  It  is  then  removed,  heated  to 
whiteness,  and  converted  into  a  solid  mass  by  hammering.  Plati- 
num is  also  melted  in  lime  crucibles,  heated  by  the  flame  of  the 
oxy hydrogen  blow-pipe  directed  against  the  mass  of  metal. 

Platinum  is  a  grayish-white,  lustrous  metal.  Its  density  is 
21.5.  It  is  very  malleable  and  ductile.  It  melts  in  the  oxy- 
hydrogen  flame  and  in  the  electric  furnace ;  at  a  white  heat  it- 
becomes  soft  and  can  be  forged  and  welded  like  iron.  It  is  not 
affected  by  the  air  at  any  temperature,  and  does  not  dissolve  in 
either  hydrochloric,  sulphuric,  or  nitric  acid.  When  alloyed 
with  silver,  it  is  attacked  by  nitric  acid.  Nitro-hydrochloric 
acid  dissolves  it  slowly  in  the  cold,  more  rapidly  by  the  aid 
of  heat,  converting  it  into  the  tetrachloride.  The  alkaline  hy- 
droxides and  nitrates  attack  it  at  a  high  temperature,  and  these 
substances  must  not  be  fused  in  platinum  crucibles. 

Platinum  has  the  power  of  condensing  gases  in  its  pores,  and 
we  have  already  seen  how  the  oxidation  of  ammonia  and  vapor 
of  alcohol  and  ether  may  be  effected  by  a  platinum  wire.  This 
property  is  more  strongly  manifested  by  platinum  sponge  than 
by  the  compact  metal,  and  hydrogen  escaping  from  a  jet  may 
be  ignited  by  holding  in  it  a  morsel  of  recently-heated  spongy 


PLATINUM   AND    ITS   ALLIED    METALS.  333 

platinum.  When  a  solution  of  platinic  chloride  is  boiled  with 
potassium  hydroxide,  and  alcohol  is  added  to  the  boiling  liquid 
with  constant  stirring,  metallic  platinum  is  deposited  as  a  black 
powder.  This  powder,  which  is  called  platinum-black,  is  in  a 
state  of  extreme  division,  and  brings  about  the  oxidation  of  com- 
bustible gases  and  vapors  even  more  readily  than  platinum  sponge. 

Platinum  is  employed  for  the  manufacture  of  crucibles  and 
dishes  for  the  laboratory,  for  it  not  only  resists  high  temperatures 
but  is  attacked  by  very  few  chemical  reagents.  It  is.  manufac- 
tured into  large  retorts  for  the  concentration  of  sulphuric  acid. 
Large  quantities  of  platinum  are  used  in  the  manufacture  of 
incandescent  electric  and  gas  lamps,  and  of  artificial  teeth. 

Platinum  forms  two  series  of  compounds, — platinous  compounds, 
in  which  it  is  diatomic,  and  platinic  compounds,  in  which  it  is 
tetratomic. 

562.  PLATINIC  CHLORIDE,  PtCl*,  is  made  by  dissolving  the 
metal  in  nitre-hydrochloric  acid.     When  the  reddish-brown  liquid 
is  sufficiently  concentrated,  it  deposits,  on  cooling,  hydrated  crys- 
tals of  platinic  chloride,  which  may  be  rendered  anhydrous  by 
heat.     The  anhydrous  salt  is  a  red-brown  deliquescent  mass,  very 
soluble  in  water,  alcohol,  and  ether.     With  hydrochloric  acid 
it  forms  the  compound  PtCl*.2HCl,  which  crystallizes  with  six 
molecules  of  water,  and  is  called  chloro-platinic  acid.    The  aque- 
ous solution  of  this  compound  produces  yellow  crystalline  precipi- 
tates in  solutions  of  potassium  and  ammonium  chlorides.    They 
are  chloroplatinates,  and  have  the  compositions  PtCl*.2KCl  and 
PtCl4.2NH4Cl.    They  are  slightly  soluble  in  cold  water,  and  in- 
soluble in  alcohol,  but  dissolve  readily  in  boiling  water.  When  the 
ammonium  salt  is  heated,  it  leaves  a  residue  of  spongy  platinum. 

If  platinum  tetrachloride  be  carefully  heated  to  200°,  chlorine 
is  disengaged;  and  if  the  residue  be  extracted  with  boiling  water, 
the  unaltered  platinic  chloride  is  dissolved,  while  platinum  dichlo- 
ride,  PtCl2,  remains  as  an  olive-green  powder. 

Of  the  other  metals  of  the  platinum  group,  OSMIUM  is  the  least  fusible :  its 
melting  point  is  about  2500°.  When  strongly  heated  in  the  air,  it  forms  a 
volatile  oxide,  which  is  one  of  the  most  dangerous  poisons  known.  It  is  the 
heaviest  known  element,  having  a  density  of  22.48. 

563.  PALLADIUM  is  the  most  fusible  of  these  metals,  and  has  the  lowest 


334  LESSONS    IN    CHEMISTRY. 

density,  its  specific  weight  being  11.4.  When  a  piece  of  this  metal  is  made 
the  negative  electrode  of  an  apparatus  in  which  water  is  being  decomposed 
by  the  voltaic  current,  it  will  absorb  about  nine  hundred  times  its  volume  of 
hydrogen. 

564.  IRIDIUM  often  constitutes  a  considerable  proportion  of  platinum  ore, 
which  is  then  called  platiniridium  or  osmiridium,  as  platinum  or  osmium  pre- 
ponderates in  the  alloy.     Iridium  alloyed  with  90  per  cent,  of  platinum  is  as 
hard  and  elastic  as  steel,  is  less  fusible  than  platinum,  and  is  unaltered  by  the 
air.     It  is  used  for  the  points  of  gold  pens  and  ink-containing  pencils,  as  is 
also  the  native  alloy,  osmiridium.     The  density  of  iridium  is  22.38. 

565.  RHODIUM  is  more  fusible  than  iridium,  but  less  fusible  than  platinum. 
Its  density  is  12.1.     It  does  not  dissolve  in  nitro-hydrochloric  acid  unless  it  is 
alloyed  with  other  metals. 

566.  RUTHENIUM  is  the  most  infusible  metal  after  osmium.     Its  density  is 
12.26.     It  is  hardly  attacked  by  boiling  nitro-hydrochloric  acid. 


LESSON    LXIII. 
THE  CHEMISTRY   OF  LIFE. 

567.  As  a  result  of  that  wonderful  activity  which  we  call 
life,  certain  chemical  compounds  undergo  a  complete  metamor- 
phosis. Their  elements  become  rearranged  in  manners  which 
are  beyond  our  methods  of  research,  and  the  matter  becomes  or- 
ganized. It  assumes  certain  definite  forms  which  we  call  cells, 
and  living  cells  are  gifted  with  a  wonderful  power  of  reproduc- 
tion :  under  the  proper  conditions  they  can  convert  unorganized 
dead  matter  into  other  cells,  either  of  the  same  kind  or  of  very 
different  kinds  related  by  progressive  modifications.  Chemists 
are  able  to  change  one  form  of  matter  into  another, — to  modify 
and  destroy  molecules,  and  to  construct  new  molecules ;  they  are 
unable  to  create  the  simplest  cell,  the  lowest  form  of  organized 
matter.  We  have  no  reason  to  believe  that  any  cell  is  ever  pro- 
duced except  from  another,  but  we  know  that  under  modified  cir- 
cumstances the  nature  of  the  cell  may  in  the  course  of  succes- 
sive reproductions  become  completely  modified,  and  new  forms  of 
organized  matter  are  produced. 

The  elements  which  enter  into  the  composition  of  organized 


THE   CHEMISTRY   OF   LIFE.  335 

matter  are  comparatively  few ;  all  vital  tissues  contain  carbon,  hydro- 
gen, and  oxygen,  and  these  three,  together  with  nitrogen  and  a  few 
salts,  principally  phosphates,  chlorides,  and  sulphates  of  sodium, 
potassium,  and  calcium,  constitute  the  greater  part  of  all  tissues, 
vegetable  and  animal.  Green  plants  under  the  influence  of  sunlight 
transform  carbon  dioxide  and  water  into  free  oxygen  and  more  com- 
plex carbon  compounds,  such  as  celluloses,  starches,  sugars,  and  even 
hydrocarbons.*  In  this  reducing  action  of  vegetable  life  on  carbon 
dioxide  and  water,  the  atoms  of  carbon  and  hydrogen  recover  part  of 
the  energy  which  disappears  from  them  in  the  formation  of  those 
compounds.  As  far  as  their  matter  is  concerned,  plants  then  act 
as  storers  or  regenerators  of  energy.  In  the  natural  heat  and 
motion  of  animals  the  atomic  energy  of  the  compounds  of  carbon 
and  hydrogen  is  manifested  as  those  compounds  are  again  oxidized 
with  the  formation  of  carbon  dioxide  and  water.  Animal  life  is 
really  dependent  on  the  continual  expenditure  of  energy.  Vege- 
tables can  receive  their  nutrition  directly  from  mineral  matter, 
but  animals  can  form  tissues  only  from  matter  that  has  first  been 
prepared  by  vegetables  or  other  animals. 

However,  besides  the  carbon,  hydrogen,  and  oxygen,  plants 
absorb  nitrogen  from  nitrogenized  matters  in  the  soil,f  and  the 
nitrogen  compounds  of  plants  are  essential  for  the  nutrition  of 
animals.  We  must  study  some  of  the  compounds  which  have 
thus  far  been  formed  only  under  the  influence  of  life,  and  of 
which  the  organization  results  in  the  production  of  cells.  Among 
these  substances,  which  we  must  remember  are  not  chemical  com- 
pounds of  definite  and  known  constitution,  of  first  importance  are 
the  albuminoid  matters. 

ALBUMINOID  AND   GELATINOID  SUBSTANCES. 

568.  These  complex  matters  are  composed  of  carbon,  hydro- 
gen, oxygen,  and  nitrogen,  and  a  small  proportion  of  sulphur. 

#  Plants  destitute  of  leaf-green,  or  chloropJiyl,  derive  their  nourishment 
from  other  plants  or  from  animals. 

f  By  the  aid  of  bacteria  existing  in  root  tubercles,  certain  plants — notably 
the  members  of  the  Pea  family — appear  to  possess  the  power  of  absorbing 
free  nitrogen  from  the  atmosphere. 


336  LESSONS   IN    CHEMISTRY. 

By  their  compositions  and  properties,  they  are  all  related  to  the 
albumen  of  white  of  egg,  or  to  the  gelatin  or  glue  which  can  be 
extracted  from  bones.  If  flour  made  from  wheat  or  other  cereal 
be  kneaded  in  water,  the  starch  is  washed  out,  while  a  gray  elastic 
mass  of  gluten  remains.  This  gluten  may  be  separated  into  sev- 
eral different  substances,  having  different  degrees  of  solubility  in 
alcohol :  they  are  of  similar  composition,  containing  a  little  more 
than  50  per  cent,  of  carbon,  7  of  hydrogen,  17  of  nitrogen,  20  of 
oxygen,  and  rather  less  than  one  per  cent,  of  sulphur.  The  water 
used  in  the  preparation  of  gluten  contains  another  matter,  which 
may  be  separated  by  allowing  the  starch  to  settle,  adding  a  few 
drops  of  acid  to  the  clear  liquid,  and  heating  to  the  boiling  point. 
An  albuminoid  matter  then  coagulates  in  white  flakes.  From  the 
seeds  of  leguminous  vegetables,  such  as  peas,  beans,  and  lentils,  a  body 
called  legumine  may  be  extracted,  and,  in  addition  to  the  elements 
contained  in  gluten  and  other  vegetable  albumens,  this  substance 
contains  a  small  percentage  of  phosphoric  acid,  in  which  various  car- 
bon groups  appear  to  replace  one  or  more  of  the  hydroxyl  groups. 

The  albuminoid  matters  of  animals,  which  are  derived  from  the 
similar  vegetable  substances,  are  classified  more  with  reference  to 
their  behavior  under  the  action  of  heat,  and  their  solubilities  in 
water,  acids,  alkalies,  etc.,  than  according  to  their  composition, 
which  varies  but  little.  They  may,  however,  be  arranged  in 
two  groups, — albuminoid  matters  and  gelatin-like  compounds. 

The  general  composition  of  these  bodies  is  as  follows : 

Albumen  Group.  Gelatin  Group. 

Carbon 53.5  50.0 

Hydrogen 6.9  6.6 

Oxygen    . 23.0  26.1  to  23.1 

Nitrogen 15.6  16.8 

Sulphur 1.0  0.5  to  3.5 

Of  the  albuminoid  matters  we  can  consider  only  albumin, 
fibrin,  casein,  and  hemoglobin. 

569.  ALBUMIN  exists  in  a  soluble  form  and  an  insoluble  modi- 
fication. Soluble,  it  occurs  in  white  of  egg,  and  in  the  serum  or 
clear  liquid  of  blood ;  but  even  these  forms  present  certain  differ- 
ences. If  either  of  these  liquids  be  evaporated  at  a  low  temper- 


ALBUMINOID    BODIES.  337 

ature,  the  albumin  remains  as  a  transparent,  yellowish,  gum-like 
mass,  which  is  perfectly  soluble  in  water.  It  is  not  pure,  but 
contains  a  small  quantity  of  alkaline  carbonate  and  certain  salts. 
If  a  solution  of  albumin  be  heated  to  70°,  it  becomes  clouded, 
and  at  a  few  degrees  higher  the  albumin  separates  either  in  flakes 
or  in  a  solid  mass,  according  to  the  concentration  of  the  solution. 
The  soluble  albumin  has  coagulated  and  has  become  insoluble 
albumin.  Solutions  of  albumin  are  also  coagulated  by  the  addi- 
tion of  either  sulphuric,  nitric,  or  hydrochloric  acid,  or  of  certain 
salts,  such  as  mercuric  chloride  and  lead  acetate.  Metaphosphoric 
acid  instantly  precipitates  albumin  from  its  solutions.  Ortho- 
phosphoric  acid,  acetic  and  lactic  acids,  form  no  precipitates  with 
albumin,  neither  does  common  salt  unless  acetic  acid  be  present. 

570.  FIBRIN. — When  fresh  blood  is  allowed  to  stand,  it  soon 
separates  into  a  yellow  liquid,  called  serum,  and  a  red  coagulum  or 
clot.     The  clot  contains  the  red  corpuscles,  the  oxygen-carriers  of 
the  blood,  imprisoned  in  a  mass  of  insoluble  albuminoid  matter. 
By  beating  the  fresh  blood  with  a  bunch  of  twigs  or  an  egg- 
beater,  the  mass  of  blood  is  prevented  from  coagulating,  and  the 
albuminoid  matter,  which  is  called  fibrin,  becomes  attached  to  the 
beater  in  red  flakes.     By  washing  in  a  stream  of  water,  the  red 
corpuscles  are  washed  out,  and  the  fibrin  remains  as  light-gray, 
elastic  filaments.     It  is  insoluble  in  water,  but  dissolves  in  very 
dilute  alkaline  solutions.     Fibrin  is  formed  by  the  union  of  two 
substances  contained  in  the  blood,  whenever  that  liquid  is  kept  at 
rest.    Its  spontaneous  coagulation  causes  the  cessation  of  bleeding 
from  slight  cuts  and  other  small  wounds. 

The  stiffening  of  the  muscles  which  takes  place  soon  after  death, 
is  due  to  the  coagulation  of  a  peculiar  albuminoid  matter,  called 
myosin,  which  exists  in  solution  in  the  muscular  tissues.  It  is 
soluble  in  water  containing  10  per  cent,  of  salt,  but  is  precipitated 
by  a  larger  quantity  :  it  is  extracted  by  virtue  of  this  property. 

571.  HEMOGLOBIN   is  a  crystallizable  matter  which  can  be 
extracted  from  the  red  corpuscles  of  blood.     It  contains  a  small 
proportion  of  iron.     Hemoglobin  has  the  property  of  absorbing 
oxygen  and  forming  an  unstable  compound  from  which  the  oxygen 

22 


338  LESSONS    IN   CHEMISTRY. 

escapes  by  exposure  in  a  vacuum.  It  is  probably  by  this  property 
of  the  hemoglobin  which  they  contain,  that  the  red  blood  cor- 
puscles are  enabled  to  carry  oxygen  to  all  parts  of  the  system. 
Hemoglobin  will  also  absorb  carbon  monoxide,  and  when  it  has 
absorbed  that  gas  it  is  incapable  of  combining  with  oxygen  :  this 
explains  the  poisonous  effects  of  carbon  monoxide  on  the  system. 
Hydrogen  sulphide  reduces  hemoglobin, — that  is,  removes  its 
oxygen ;  and  we  can  so  understand  the  injurious  action  of  any 
quantities  of  this  gas. 

572.  CASEIN,  MILK. — Milk  is  a  dilute  solution  of  lactose  or 
milk  sugar  and  a  small  quantity  of  mineral  salts,  in  which  are 
suspended  very  small  fat  globules,  and,  either  suspended  or  in 
solution,  an  albuminoid  matter  called  casein.  The  specific  gravity 
of  milk  is  about  1.030.  After  standing  for  several  hours,  the 
greater  number  of  the  fat  globules  come  to  the  surface,  consti- 
tuting the  cream ;  cream,  however,  contains  some  lactose,  casein, 
and  salts.  Its  composition  varies  greatly,  as  may  be  seen  from  the 
following  results  of  the  analysis  of  three  samples : 

i.  n.  in. 

Water 72.2  66.36  50 

Fat 19.0  18.87  43.9 

Casein,  lactose,  salts 8.8  14.77  6.1 

The  following  is  the  composition  of  an  average  sample  of  cow's 
milk,  but  it  must  be  borne  in  mind  that  no  two  samples  will  prob- 
ably have  exactly  the  same  composition : 

Water 87.0  per  cent. 

Fat 3.5       " 

Lactose 4.8       " 

Casein 4.0        " 

Salts 0.7       " 

"When  an  acid  is  added  to  milk,  a  thick  deposit  of  coagulated 
casein  is  formed.  This  same  precipitation  occurs  when  milk 
naturally  becomes  sour  by  the  formation  of  lactic  acid.  Casein 
closely  resembles  insoluble  albumin  ;  it  is  insoluble  in  water, 
but  dissolves  in  dilute  solutions  of  the  alkaline  hydroxides  and 
carbonates,  and  it  is  probably  in  solution  in  fresh  milk,  for  that 
liquid  has  an  alkaline  reaction.  Casein  is  the  characteristic 
constituent  of  cheese. 


THE   CHEMISTRY   OF   LIFE.  339 

In  cheese-making,  rennet,  a  substance  obtained  from  the  fourth 
stomach  of  the  calf,  is  added  to  the  milk :  this  precipitates  the 
casein,  and  the  latter,  enveloping  the  fat-globules,  carries  them 
down  with  it.  The  curd,  separated  from  the  liquid,  constitutes 


573.  GELATIN. — When  bones  are  immersed  in  hydrochloric 
acid,  the  mineral  matter,  consisting  principally  of  calcium  phos- 
phate and  carbonate,  is  dissolved,  and  a  semi-transparent,  elastic 
mass  is  obtained,  retaining  the  form  of  the  bone.     This  body  is 
insoluble  in  cold  water,  but  by  long  boiling  it  dissolves,  and,  on 
cooling,  the  solution  sets  in  a  transparent  jelly.     This  substance 
is  gelatin,  or  glue.     It  is  not  peculiar  to  the  bones,  but  exists  also 
in  certain  other  tissues,  particularly  in  the  skin,  and  in  the  swim- 
ming-bladders of  fishes.     The  best  gelatin  is  obtained  from  the 
swimming-bladder  of  the  sturgeon ;  it  is  called  fish-glue.     Very 
little  is  known  regarding  the  difference  between  gelatin  and  the 
substances  from  which  it  is  derived. 

Dry  gelatin  occurs  in  transparent  or  translucent  sonorous  sheets, 
whose  color  varies  from  colorless  to  brown,  according  to  the  purity. 
It  swells  in  water,  but  does  not  dissolve  until  the  liquid  is  heated. 
Its  solution  is  precipitated  by  alcohol,  but  not  by  acids,  with  the 
exception  of  tannic  acid,  with  which  it  forms  an  insoluble  com- 
pound. The  tanning  of  skins  and  hides  depends  on  the  formation 
of  this  compound  in  the  body  of  the  skin,  which  is  so  converted 
into  leather. 

574.  By  the  processes  of  digestion,  the  vegetable  and  animal 
matters  which  serve  as  food  are  converted  into  substances  which 
can  be  assimilated  or  made  part  of  our  bodies.     These  processes 
begin  in  the  mouth,  where  the  starchy  substances  encounter  in 
the  saliva  a  peculiar  unorganized  ferment  called  ptyalin,  which  is 
capable  of  transforming  them  into  soluble  glucose.     Ptyalin  is 
probably  identical  with  diastase,  which  is  formed  during  the  germi- 
nation of  grain.     In  the  stomach,  the  conversion  of  starch  into 
glucose  continues,  and  the  albuminoid  matters  are  converted  into 
soluble  bodies  called  peptones  by  another  ferment,  pepsin,  contained, 


340  LESSONS    IN   CHEMISTRY. 

together  with  a  little  hydrochloric  acid,  in  the  gastric  juice.  This 
ferment  exists  in  rennet,  obtained  from  the  stomach  of  the  calf, 
and  used  in  the  manufacture  of  cheese.  The  peptones  appear  to 
be  formed  by  the  hydration  of  the  albuminoid  bodies,  and  in 
the  system  they  are  probably  converted  into  all  the  varieties  of 
albuminoid  tissue.  As  the  food  passes  from  the  stomach  it 
encounters  in  the  small  intestines  other  ferments,  by  which  the 
fatty  matters  are  emulsified  and  rendered  capable  of  being  ab- 
sorbed and  passing  into  the  blood,  by  which  they  are  carried 
and  deposited  where  needed  in  the  system. 

The  slow  combustion  by  which  life  is  sustained  results  in  the 
oxidation  of  the  tissues,  and  the  removal  of  the  matters  no  longer 
useful.  This  oxidation  is  not  accomplished  in  one  operation,  but 
in  several  stages,  during  which  many  compounds  intermediate 
between  the  albuminoid  and  fatty  bodies,  and  the  carbon  dioxide, 
water,  and  nitrogen  which  would  result  from  their  complete  com- 
bustion, are  formed.  We  have  seen  that  a  great  part  of  the  carbon 
and  hydrogen  is  indeed  removed  as  carbon  dioxide  and  water,  but 
the  salts  are  in  great  part  eliminated  unchanged  by  the  urine  and 
the  perspiration.  The  nitrogen  is  excreted  principally  as  urea, 
phosphorus  as  sodium  acid  phosphate,  sulphur  as  sodium  sulphate, 
etc.  A  small  part  of  the  nitrogen  of  the  system  is  excreted  in 
forms  intermediate  between  the  albuminoid  bodies  and  urea. 
Among  the  more  important  of  these  is  uric  acid,  C5H4N403,  a 
compound  forming  a  small  proportion  of  human  urine,  and  exist- 
ing in  large  quantity  in  the  solid  urine  of  birds  and  reptiles. 

In  all  these  processes  there  is  comparatively  little  that  we  can 
understand.  We  know  only  that  they  all  result  in  a  transfer  of 
energy, — that  in  living  matter  the  chemical  energy  is  converted 
into  the  energy  of  life  ;  and  we  can  comprehend  only  the  beginning 
and  the  end  of  the  phenomenon, — the  forms  of  matter  which  are 
capable  of  organization,  and  the  products  of  the  disorganization 
without  which  life  could  not  continue. 


APPENDIX. 


CKYSTALLOGKAPHY. 

A  crystal  is  a  natural  polyhedron  ;  that  is,  a  solid  bounded  by  plane 
surfaces  or  faces.  The  greater  number  of  solid  chemical  substances 
form  more  or  less  perfect  crystals  whenever  a  certain  freedom  of  mo- 
tion is  communicated  to  their  molecules,  so  that  these  molecules  may 
arrange  themselves  without  interference.  Such  freedom  of  motion 
may  be  given  to  the  molecules : 

1.  By  dissolving  the  solid  in  any  liquid  by  which  it  is  not  altered, 
and  allowing  a  hot  saturated  solution  to  cool  slowly,  or  by  the  spon- 
taneous evaporation  of  the  solvent  if  the  solid  be  equally  soluble  at 
all  temperatures.     Potassium  chlorate,  lead  iodide,  potassium  nitrate, 
and  alum  may  be  crystallized  from  water  by  the  first  method ;  com- 
mon salt  by  the  second. 

2.  By  melting  the  solid,  and  decanting  the  still  liquid  portion  after 
a  crust  has  formed  on  its  surface.     Sulphur  and  bismuth  may  be  so 
crystallized. 

3.  By  subliming  the  solid,  and  allowing  the  vapor   to  condense 
very  slowly.      In  this  manner  fine  crystals  of  iodine  and  camphor 
may  be  obtained. 

4.  By  a  chemical  reaction  in  which  the  crystallizable  substance  is 
formed  in   a  medium  in  which   it  is  insoluble.     Potassium  chloro- 
platinate  and  potassium   acid  tartrate   are  so  formed  in  microscopic 
crystals. 

A  solid  which  manifests  no  tendency  to  become  crystalline  is  said 
to  be  amorphous.  Glass  and  glue  are  examples  of  amorphous  sub- 
stances. 

For  the  sake  of  convenience  crystals  are  classified  in  six  systems,  and 

341 


342 


APPENDIX. 


each  system  is  characterized  by  a  set  of  axes,  which  are  imaginary 
straight  lines  passing  through  the  centre  of  the  crystal  and  joining 
opposite  solid  angles  or  the  centres  of  opposite  faces  or  edges.  The 
forms  belonging  to  any  one  system  may  be  derived  from  each  other 
by  replacing  the  edges  or  angles  by  plane  surfaces  ;  in  all  such  deriva- 
tives the  imaginary  axes  must  remain  unchanged. 

1.  THE  ISOMETRIC  SYSTEM  has  three  equal  axes  at  right  angles  to 
each  other.  The  type  of  the  system  is  the  octahedron  (a),  in  which 
the  axes  join  the  opposite  angles.  The  tetrahedron  (6)  is  derived  from 


this  form  by  extending  the  alternate  faces  until  they  meet,  forming 
edges  of  which  the  centres  are  then  joined  by  the  axes.  The  cube  (c) 
is  obtained  by  replacing  or  truncating  the  six  angles  of  the  octahedron 
by  as  many  faces,  and  extending  these  until  they  form  edges ;  the 
axes  join  the  centres  of  opposite  faces.  By  replacing  or  bevelling  the 


1L 


twelve  edges  of  the  octahedron  by  the  same  number  of  faces  so  that 
these  meet  in  the  centres  of  the  octahedral  faces,  the  rhombic  dodeca- 
hedron (d)  is  produced. 

Besides  these  simpler  forms,  the  isometric  system  includes  a  number 
of  others  which  are  bounded  by  twelve,  twenty-four,  and  even  forty- 
eight  facea. 


APPENDIX. 


343 


2.  THE  TETRAGONAL  SYSTEM  is  characterized  by  three  axes  inter- 
secting at  right  angles,  of  which  two  are  equal  and  the  third  either 


longer  or  shorter.  The  type  is  the  tetragonal  pyramid  (e),  in  which 
the  axes  join  the  opposite  angles.  A  similar  form  (/),  in  which  two 
of  the  axes  connect  the  centres  of  opposite  edges,  while  the  third  axis 


\ 


4- 


joins  the  vertices,  is  called  a  pyramid  of  the  second  order.  Prisms 
of  the  first  (g)  and  of  the  second  (A)  order,  as  well  as  more  complex 
forms,  occur  in  this  system. 

3.  THE  ORTHORHOMBIC  SYSTEM  has  three  unequal  axes  at  right 
angles  to  each  other.  The  typical  form  is  the  orthorhombic  pyramid 
(i),  in  which  the  axes  connect  the  opposite  angles.  Other  forms  of 
this  system  are  designated  as  prisms  (&),  domes,  and  pinacoids. 


344 


APPENDIX. 


4.  THE  HEXAGONAL  SYSTEM  has  four  axes ;  three  are  in  the  same 
plane,  equal  in  length,  and  intersect  at  angles  of  60°  ;  the  fourth  is  at 


(k) 


right  angles  to  these  three,  and  may  be  either  longer  or  shorter.     In 
the  typical  form,  the  hexagonal  pyramid  of  the  first  order  (I),  the  four 


axes  join  the  solid  angles  ;  in  the  pyramid  of  the  second  order  (m),  the 
three  equal  axes  connect  the  centres  of  opposite  edges,  while  the  fourth 


axis  joins  the  two  vertices.     The  commonest  form  of  this  system,  the 
rhombohedron   (w),  results   from   the  pyramids  by  extending  their 


APPENDIX.  345 

alternate  faces  till  they  meet :  it  is  bounded  by  six  rhombus-shaped 


Prisms  of  the  first  (o)  and  second  order  (jo),  and  other  more  com- 
plex forms,  belong  to  this  system. 

5.  THE  MONOCLINIC  SYSTEM  has  three  unequal  axes,  of  which  two 
are  obliquely  inclined  to  each  other  in  a  plane  intersecting  the  third 
axis  at  right  angles.  The  plane  containing  the  first  two  axes  divides 
the  forms  of  this  system  into  symmetrical  halves  :  monoclinic  crystals 
are  characterized  by  their  bilateral  symmetry. 

Monoclinic  pyramids  (q]  have  two  sets  of  faces.  There  are  also 
prisms,  domes,  and  pinacoids.  ,. 


6.  THE  TRICLINIC  SYSTEM  has  three  unequal  axes  which  are  ob- 
liquely inclined  to  each  other. 

The  names  of  the  triclinic  forms  are  analogous  to  those  of  the  or- 
thorhombic  and  monoclinic  systems. 

The  crystal  forms  enumerated  above  are  either  closed  forms  or  open 
forms.  The  former  may  exist  by  themselves,  as,  for  example,  a  cube 
or  a  rhombohedron,  while  the  latter  require  one  or  several  other  forms 
to  enclose  space.  Most  of  the  natural  crystals  show  combinations  of 
several  forms,  modifying  each  other  in  various  manners.  The  char- 
acteristic axes,  however,  are  not  aifected  by  these  modifications. 

A  substance  which  crystallizes  in  forms  belonging  to  two  different 
systems  is  said  to  be  dimorphous.  Such  a  body  is  sulphur. 

Two  different  substances  whose  crystals  are  of  precisely  the  same 
form  are  said  to  be  isomorphous.  The  chlorides,  bromides,  and 
iodides  of  potassium  and  sodium  are  isomorphous  ;  the  alums  and  the 
spinels  are  also  excellent  examples  of  isomorphism. 


346  APPENDIX. 

II. 

STEREOCHEMISTRY. 

Of  the  very  numerous  cases  of  isomerism  which  have  been  observed 
among  the  carbon  compounds,  the  great  majority  may  be  explained  by 
assigning  different  molecular  structure  to  the  different  compounds  of 
the  same  composition.  Structural  formulae  are  employed  to  represent 
the  relations  supposed  to  exist  between  the  atoms  constituting  the 
molecules.  A  few  instances,  however,  have  long  been  known  of  com- 
pounds whose  constitution  must  be  expressed  by  the  same  structural 
formula,  although  they  differ  in  certain  of  their  properties.  The 
lactic  acids  (see  p.  216)  afford  an  example  of  this  mode  of  isomerism. 
Ordinary  lactic  acid,  which  is  produced  in  the  lactic  fermentation  of 
sugar,  when  dissolved  in  water  has  no  action  upon  polarized  light, 
while  solutions  of  the  other  two  modifications  have  the  property  of 
rotating  the  plane  of  polarization  :  sarcolactic  or  dextrolactic  acid  de- 
flects it  to  the  right,  and  levolactic  acid  to  the  left.  In  the  formula 
CH3.CH(OH).COOH,  one  of  the  carbon  atoms  is  combined  with  an 
atom  of  hydrogen,  and  with  one  of  each  of  the  radicals  hydroxyl, 
methyl,  and  carboxyl ;  the  four  atomicities  of  this  carbon  atom  are  em- 
ployed in  uniting  four  different  atoms  or  groups  with  it. 

H 

CH3— C— OH 
COOH 

It  has  been  shown  that  all  the  other  known  carbon  compounds  which 
are  optically  active  (rotate  the  plane  of  polarized  light)  contain  one 
or  more  such  carbon  atoms,  and  further,  that  these  compounds  always 
exist  in  several  modifications.  To  account  for  these  remarkable  facts 
the  following  theory  has  been  proposed. 

All  the  known  facts  indicate  that  the  four  atomicities  of  the  carbon 
atom  are  exactly  alike.  Now,  if  we  conceive  an  atom  to  be  so  situated 
as  to  form  the  centre  of  an  isometric  tetrahedron,  and  the  four  atoms  or 
groups  with  which  the  atom  is  united,  at  the  vertices  of  this  tetrahe- 
dron, the  affinities  would  be  symmetrically  distributed. 

As  long  as  any  two  atoms  or  groups  of  the  same  kind  occupy  posi- 
tions at  the  vertices,  only  one  form  is  possible  ;  *  but  when  the  four 


*  This  can  only  be  shown  by  means  of  stereochemical  models. 


APPENDIX. 


347 


atoms  or  groups  are  all  different,  these  may  be  arranged  in  two  differ- 
ent ways :  the  two  resulting  systems  cannot  be  made  to  coincide  by 
rotation,  one  being  to  the  other  as  an  object  is  to  its  mirror  image. 


The  carbon  atom  at  the  centre  of  the  tetrahedron  is  then  said  to  be 
asymmetric. 

The  two  optically  active  modifications  of  lactic  acid  would  corre- 
spond to  the  two  arrangements,  or  configurations. 


COO 


CM3 


COOHN 


OH 


Inactive  lactic  acid  may  be  resolved  into  the  active  varieties,  and 
must  be  regarded  as  resulting  from  the  combination  of  equal  propor- 
tions of  these  :  the  rotary  power  of  the  one  would  then  be  compensated 
by  that  of  the  other. 

When  a  molecule  contains  two  asymmetric  carbon  atoms,  the  theory 
predicts  four  modifications  of  the  compound.  In  the  case  of  tartaric 
acid,  COOH.CH(OH).CH(OH).COOH,  the  four  forms  are  actually 
known.  There  are  two  active  varieties,  dextrotartaric  acid  and  levo- 
tartaric  acid,  each  of  which  contains  two  exactly  similar  asymmetric 
carbon  atoms  ;  and  of  the  two  inactive  modifications,  mesotartaric  acid 
contains  two  carbon  atoms  of  opposite  rotary  power,  while  racemic 
acid  (which  can  be  split  up  into  the  dextro-  and  levo-forms)  is  com- 
posed of  equal  proportions  of  the  two  active  tartaric  acids. 


348  APPENDIX. 

This  kind  of  isomerism,  which  is  attributed  to  a  different  relative 
arrangement  of  the  atoms  in  space,  is  called  stereoisomerism,  and  that 
branch  of  theoretical  chemistry  which  seeks  to  determine  these  spacial 
relations,  stereochemistry. 

Stereoisomerism  is  not  confined  to  those  substances  which  contain 
asymmetric  carbon  atoms  :  many  cases  are  also  known  among  the  un- 
saturated  carbon  compounds,  and  in  certain  classes  of  bodies  contain- 
ing nitrogen. 


INDEX. 


Acetates,  210. 

Acetone,  210. 

Acetylene,  186. 

Acid,  acetic,  C2H*02,  194,  207. 

acrylic,  C3H*02,  216. 

antimonic,  135. 

arsenic,  130. 

arsenious,  H3As03,  130. 

benzoic,  C7H6Q2,  231. 

boric,  H3B03,  138. 

butyric,  OH802,  210. 

carbolic,  226. 

carbonic,  H2C03,  156. 

chloric,  HC103,  67. 

chloroplatinic,  PtC.l*.2HCl,  333. 

chromic,  H2CrO±,  326. 

citric,  C«H807,  219. 

cyanic,  HOCN,  171. 

cyanuric,  N3C303H3,  172. 

digallic,  C"Hl°0»,  233. 

ethylsulphuric,  C2H5.HS04,  203. 

formic,  CH202,  168,  193,  207. 

gallic,  C7H605,  232. 

hydracrylic,  C3H603,  216. 

hydrazoic,  N3H,  100. 

hydriodic,  HI,  71. 

hydrobromic,  HBr,  69. 

hydrochloric,  HC1,  62. 

hydrocyanic,  HCN,  166. 
tests  for,  167. 

hydrofluoric,  HF,  71. 

hydrofluosilicic,  H2SiF6,  142. 

hypochlorous,  HC10,  65. 

hypophosphorous,  H3P02,  124. 

hyposulpnurous,  H2S203,  81. 

lactic,  C3H<503,  216. 

lauric,  Ci2H2*02,  215. 


Acid,  malic,  C*K60*,  218. 
manganic,  H2MnO*,  323. 
metaboric,  HBO2,  139. 
metantimonic,  HSbO3,  135. 
metaphosphoric,  HPO3,  127. 
metarsenic,  HAsO3,  130. 
myristic,  C14H2802,  215. 
nitric,  HNO3,  112. 
nitro-hydrochloric,  114. 
nitrous,  HNO2,  108. 
oleic,  C'8H3*02,  213. 
ortharsenic,  H3AsO*,  130. 
orthophosphoric,  H3P04,  125. 
oxalic,  C2H204,  216. 
palmitic,  C16H3202,  212. 
permanganic,  HMnO4,  324. 
phosphoric,  125. 
phosphorous,  H3P03,  125. 
picric,  C6H2(N02)3OH,  227. 
propionic,  C3H6Q2,  210. 
pyroantimonic,  H4Sb207,  135. 
pyroarsenic,  H*As207,  130. 
pyrogallic,  C6H3(OH)3,  232. 
pyrophosphoric,  H*P207,  127. 
salicylic,  C6H*.OH(C02H),  232. 
silicic,  142. 
stannic,  330. 
stearic,  C18H36Q2,  213. 
succinic,  OH6Q*,  218. 
sulphocarbonic,  H2CS3,  163. 
sulphuric,  H2SO*,  82. 

fuming,  H2S20T,  81. 

molecular  structure  of,  85. 
sulphurous,  H2S08,  80. 
tannic,  233. 
tartaric,  C4H606,  218. 
tetraboric,  H2B*07,  139. 
349 


350 


INDEX. 


Acid,  thiocyanic,  HSCN,  174. 

thiosulphuric,  H2S203,  81. 

uric,  C5H*N*0*  239,  340. 

valeric,  C5H«>02,  211. 
Acids,  51,  64. 

dibasic,  88,  216. 

fatty,  210,  212. 

of  carbon,  207. 
Acrolein,  C3H*0,  210. 
Affinity,  13. 
Agate,  140. 
Air,  92. 

carbon  dioxide  in,  95. 

water  in,  94. 
Alabaster,  89. 
Albite,  305. 
Albumin,  336. 
Albuminoid  substances,  335. 
Alcohol,  amyl,  C5Hn.OH,  198. 

benzyl,  CW.CIPOH,  230. 

butyl,  OH9.0H,  198. 

ethyl,  C2fl5.0H,  193. 
absolute,  194. 

methyl,  CH8.OH,  192. 

propyl,  C3H7.0H,  197. 
Alcoholic  beverages,  195. 
Alcohols,  192. 

diatomic,  199. 

primary,  197. 

secondary,  197. 

tertiary,  198. 

triatomic,  200. 
Aldehyde,  C2H*0,  194,  206. 

salicylic,  C«H*.OH.CHO,  231. 
Aldehydes,  206. 
Aldoses,  222. 
Ale,  196. 
Alizarin,  190. 
Alkali,  246. 
Alkaloids,  236. 
Alloys,  242. 
Alumina,  A1203,  303. 
Aluminium,  301. 

bronze,  302. 

chloride,  A1C13,  302. 


Aluminium  hydroxide,  Al(OH)3,  303. 

oxide,  A1203,  303. 

silicates,  305. 

sulphate,  A12(SO*)3,  303. 

tests  for,  306. 
Alums,  304. 
Amalgams,  242. 
Amethyst,  140. 
Amides,  173. 
Amines,  173,  229. 
Ammonia,  NH3,  97. 

analysis  of,  99. 

combustion  of,  99. 
Ammonium  alum,  304. 

amalgam,  103. 

carbonates,  161. 

chloride,  NH*C1,  101. 

chloroplatinate,  333. 

compounds,  100. 

cyanate,  NH4O.CN,  172. 

dichromate,  (NH4)2Cr207,  327. 

molybdate,  (NH4)2MoO<,  128. 

nitrate,  NH*.N03,  104. 

oxalate,  (NH4)2C20*,  117. 

phosphomolybdate,  128. 

picrate,  NH*.OC6H2(N02)3,  228. 

sulphate,  (NH)2SO*,  102. 

sulphide,  (NH*)*S,  102. 

sulphocyanate,  NH*NCS,  175. 

sulphydrate,  NH*SH,  102. 

thiocyanate,  175. 
Amygdalin,  231. 
Amyl  acetate,  C5H».C2H302,  212. 

alcohols,  CWi.OH,  198. 
Amylene,  C5H10,  185. 
Analysis,  33. 

of  carbon  compounds,  190. 
Anatase,  331. 
Anglesite,  91. 
Aniline,  C6R5.NH2,  228. 

colors,  230. 

Anthracene,  C^HW,  190. 
Anthracite,  145. 
Antichlor,  81. 
Antimony,  134. 


INDEX. 


351 


Antimony  chlorides,  135. 

oxides,  135. 

trisulphide,  135. 
Apatite,  127. 
Aragonite,  160. 
Argol,  218. 
Argon,  94. 

Aromatic  compounds,  189. 
Arsenic,  128. 

chloride,  AsCl3,  129. 

disulphide,  As2S2,  130. 

pentasulphide,  As2S5,  130. 

pentoxide,  As205,  130. 

tests  for,  131. 

trioxide,  As*06,  129. 

trisulphide,  As2S3,  130. 
Arsenic  oxide,  As205,  130. 
Arsenious  oxide,  As*06,  129. 
Asbolite,  319. 
Atacamite,  288. 
Atmosphere,  92. 
Atomic  heats,  250. 

theory,  40. 

weights,  determination  of,  41 . 
Atomicity,  theory  of,  71,  78,  86,  110, 
136,  163,  178,  187,  197,  205,  245, 
257,  265,  272,  287,  291,  302. 
Atropine,  C"H23N03,  239. 
Auric  chloride,  AuCl3,  300. 
Avogadro's  law,  39. 
Azurite,  289. 

Baking  powders,  159. 
Barium,  270. 

carbonate,  BaCO3,  160. 

chloride,  BaCl2,  270. 

dioxide,  BaO2,  271. 

hydroxide.  Ba(OH)2,  51. 

hypophosphite,  124. 

monoxide,  BaO,  270. 

nitrate,  Ba(N03)2,  118. 

sulphate,  BaSO*,  89. 

sulphide,  BaS,  270. 

tests  for,  271. 
Bases,  51. 


Beer,  196. 
Bell-metal,  287. 
Benzaldehyde,  C6H*CHO,  230. 
Benzene,  C6H6,  187. 

derivatives,  226. 
Benzine,  182. 
Benzyl  alcohol,  C«H5.CH2OH,  230. 

chloride,  C6H5.CH2C1,  231. 
Beryl,  277. 
Bessemer  process,  312. 

basic,  313. 
Bismuth,  295. 

chloride,  Bid3,  296. 

nitrate,  Bi(N03)3,  296. 

oxide,  Bi203,  296. 

sulphide,  Bi2S3,  296. 

tests  for,  297. 
Bitter  almond  oil,  231. 
Bituminous  coal,  145. 
Blende,  278,  282. 
Blue  vitriol,  CuSO4,  90. 
Bone-black,  148. 
Borax,  Na2B40',  139. 
Borneol,  C^H^O,  235. 
Boron,  137. 

chloride,  BC13,  138. 

crystallized,  138. 

oxide,  B»03,  137. 

tests  for,  140. 
Brandy,  196. 
Brass,  287. 
Braunite,  322. 
Britannia  metal,  329. 
Bromides,  248. 
Bromine,  68. 
Bromoform,  CHBr3,  206. 
Bronze,  287. 
Brook ite,  331. 
Brucine,  240. 
Bunsen  burner,  31. 
Butyl  alcohols,  OH».OH,  198. 
Butylenes,  OH8,  185,  186. 

Cacodyl,  As2(CH3)*,  210. 
Cadmium,  283. 


352 


INDEX. 


Cadmium  ferrocyanide,  Cd2(FeC6N6), 
283. 

iodide,  Cdl2,  283. 

oxide,  CdO,  283. 

sulphide,  CdS,  283. 

tests  for,  283. 
Caesium,  257. 
Caffeine,  C8H'°N402,  238. 
Calcite,  160. 
Calcium,  265. 

acetate,  208. 

carbide,  CaC2,  269. 

carbonate,  CaCO3,  160. 

in  hard  water,  49,  156. 

chloride,  CaCl2,  265. 

citrate,  220. 

hydroxide,  Ca(OH)2,  267. 

hypochlorite,  Ca(ClO)2,  66. 

lactate,  Ca(C3H5Q3)2,  216. 

phosphates,  126. 

phosphide,  123. 

sulphate,  CaSO4,  89. 
in  hard  water,  49. 

tests  for,  269. 
Calomel,  Hg2Cl2,  292. 
Camphor,  234. 
Camphors,  234. 
Cane  sugar,  C12H220",  222. 
Caramel,  222. 

Carbamide,  CO(NH2)2,  173. 
Carbohydrates,  220. 
Carbon,  144. 

atomicity  of,  163. 

compounds,  analyses  of,  190. 

dioxide,  CO2,  153. 
in  air,  95. 
tests  for,  156. 

disulphide,  CS2,  162. 

hydrates  of,  220. 

monoxide,  CO,  150. 

compounds  of,  171. 

oxy sulphide,  COS,  164. 

reduction  by,  150. 
Carbonates,  156. 

test  for,  157. 


Carbonyl  amide,  CO(NH2)2,  173. 

chloride,  COC12,  153. 

compounds  of,  171. 
Carboxyl,  207. 
Case-hardening,  314. 
Casein,  338. 
Cassiterite,  328. 
Cast  iron,  311. 
Caustic  soda,  253. 
Celestite,  89,  269. 
Celluloid,  226. 
Cellulose,  (C6H1005)n,  225. 

nitro-,  223. 
Cement,  267. 
Cerite,  306. 
Cerium,  306. 
Cerusite,  118,  272. 
Chalcedony,  140. 
Chaicocite,  284. 
Champagne,  196. 
Charcoal,  147. 

absorbent  properties  of,  149. 

animal,  147. 

filter,  149. 
Cheese,  339. 
Chemical  affinity,  13. 

changes,  8. 

combination,  11. 

energy,  152. 

equations,  42. 

formulas,  42. 

laws  and  theories,  35,  38. 

nomenclature,  50,  61,  66. 

notation,  42. 
Chloral,  C2C13HO,  207. 
Chlorates,  66. 
Chlorides,  61,  248. 

test  for,  62. 
Chlorine,  57. 

analogies     with     bromine     and 

iodine,  71. 

Chloroform,  CHC13,  206. 
Chromates,  326. 

test  for,  328. 
Chrome  green,  325. 


INDEX. 


353 


Chrome  yellow,  327. 
Chromite,  325. 
Chromium,  325. 

alum,  304. 

chlorides,  325. 

oxides,  325. 

tests  for,  327. 

Chromyl  chloride,  Cr02Cl2,  328. 
Cinchona  bark,  239. 
Cinchonine,  C»»H»2N20,  240. 
Cinnabar,  290,  294. 
Clay,  305. 
Cleveite,  245. 
Coal,  145. 

-mine  explosions,  176. 

tar,  187. 
Cobalt,  319. 

blue,  320. 

chloride,  CoCl2,  319. 

oxides,  319. 

tests  for,  320. 
Cobaltite,  319. 
Cocaine,  C17H21N04,  239. 
Codeine,  C18H«N03,  239. 
Colcothar,  317. 
Collodion,  226. 
Combination,  laws  of,  35,  38. 
Combustion,  26. 

slow,  31. 

Compound  ammonias,  236. 
Compounds,  9. 
Conine,  C8fl"N,  237. 
Copper,  283. 

acetate,  Cu(C2H302)2,  210. 

action  of  ammonia,  287. 

alloys  of,  287. 

arsenite,  CuHAsO3,  132. 

atomicity  of,  287. 

carbonates,  289. 

chlorides,  287. 

matte,  285. 

metallurgy  of,  284. 

electrolytic  process,  285. 
wet  process,  286. 

nitrate,  Cu(N03)2,  118. 


Copper  oxides,  289. 

pyrites,  284. 

sulphate,  CuSO4,  90. 

sulphides,  289. 

tests  for,  289. 
Copperas,  FeSO4,  90. 
Corrosive  sublimate,  HgCl2,  292. 
Corundum,  A1203,  303. 
Cream,  339. 
Cream  of  tartar,  219. 
Cresols,  230. 
Crocoite,  325. 
Cryolite,  72. 
Crystallization,  341. 

water  of,  47. 
Crystallography,  341. 
Cupellation,  259. 
Cupric  chloride,  CuCl2,  288. 

ferrocyanide,  Cu2(FeC6N6),  289. 

nitrate,  Cu(N03)2,  118. 

oxide,  CuO,  288. 

sulphate,  CuSO4,  90. 

sulphide,  CuS,  288. 
Cuprite,  288. 
Cuprous  chloride,  Cu2Cl2,  288. 

oxide,  Cu20,  288. 

sulphide,  Cu2S,  289. 
Cyamelide,  172. 
Cyanogen,  (CN)2,  164. 

chloride,  (CN)3C13,  172. 

molecular  structure  of,  165. 
Cymene,  C10H14,  234. 

Dalton's  law,  36. 
Daturine,  C17H23N08,  239. 
Decomposition,  11. 

double,  15. 

Definite  proportions,  laws  of,  36. 
Dextrin,  224. 
Dextrose.    See  Glucose. 
Dialysis,  142. 
Diamond,  144. 
Diastase,  222,  339. 
Didymium,  306. 
Digestion,  339. 


23 


354 


INDEX. 


Dimethylamine,  (CH3)2HN,  229. 
Dimorphism,  75,  343. 
Disaccharides,  223. 
Dolomite,  247. 
Dynamite,  200. 

Earthy  cohalt,  319. 
Elements,  9. 

table  of,  44. 
Elutriation,  282. 
Emerald,  277. 
Emery,  303. 
Epsom  salt,  MgSO4,  90. 
Equivalent    combining    proportions, 

38. 

Erbium,  306. 
Ethane,  C2H6,  179. 
Ether,  (C2R5)20,  201. 
Ethers,  compound,  211. 

simple,  201. 
Ethyl  acetate,  C2H5.C2H302,  211. 

bromide,  C2H5Br,  205. 

formate,  C2H&.CH02,  212. 

hydrate,  C2H5.0H,  193. 

iodide,  C2H5I,  204. 

nitrate,  C2H5.N03,  212. 

oxide,  (C2H5)20,  201. 

valerate,  C'H5.C5H9Q2,  212. 
Ethylene,  C2H*,  184. 

bromide,  C2H*Br2,  185. 

chloride,  C2H4C12,  184. 

cyanide,  C2H*(CN)2,  218. 

hydrate,  C2H*(OH)2,  199. 

oxide,  C2H*0,  204. 
Ethylidene  bromide,  C2H4Br2,  206. 

Fats,  natural,  213. 
Fehling's  solution,  221. 
Feldspar,  305. 
Fermentation,  acetic,  209. 

alcoholic,  193. 

lactic,  216. 
Ferric  chloride,  Fed3,  316. 

ferrocyanide,  Fe*(FeC«N  )3, 170. 

oxide,  Fe'O3,  317. 


Ferric  sulphate,  Fe2(S04)8,  318. 

thiocyanate,  174. 
Ferrocyanides,  169. 
Ferromanganese,  311. 
Ferrous  carbonate,  FeCO3,  160,  307. 

chloride,  FeCl2,  316. 

ferricyanide,  Fe3(FeC6N6)2,  171. 

oxide,  FeO,  316. 

sulphate,  FeSO4,  90. 
Fibrin,  337. 
Fire,  29. 
Fire-damp,  176. 
Fireworks,  271. 
Flame,  30,  176. 
Fluorine,  71. 
Fluor-spar,  CaF2,  72. 
Formates,  208. 
Formulae,  chemical,  42. 
Fractional  distillation,  187. 
Fructose,  C6H1206,  221. 
Fuller's  earth,  305. 
Fulminates,  195. 
Fusible  metal,  296. 

Gadolinite,  306. 
Galactose,  CCH^O6,  223. 
Galena,  272. 
Gallium,  300. 
Garnet,  305. 
Gas  carbon,  147. 

illuminating,  145. 

liquor,  101,  147. 
Gases,  manipulation  of,  20. 

molecular  volumes  of,  39. 
Gasoline,  182. 
Gay-Lussac's  laws,  36,  38. 
Gelatin,  339. 

Gelatinoid  substances,  335. 
Germanium,  331. 
German  silver,  287,  321. 
Gilding,  300. 
Gin,  197. 
Giobertite,  160. 
Glass,  141. 

etching  on,  71. 


INDEX. 


355 


Glucinum,  277. 
Glucose,  C6H>2Q6,  193,  220. 
Glue,  339. 
Gluten,  223,  336. 
Glycerol,  C3H5(OII)3,  199. 

ethers  of,  213. 
Glycol,  C2H4(OH)2,  199. 
Glycols,  198. 
Goethite,  307,  317. 
Gold,  297. 

assay,  300. 

chlorides,  299. 

oxides,  300. 
Graphite,  144. 
Greenockite,  283. 
Green  vitriol,  FeSO4,  90. 
Gum  arabic,  225. 
Gums,  224. 

Gum  tragacanth,  225. 
Gun-cotton,  225. 
Gun  metal,  287. 
Gunpowder,  117. 
Gypsum,  89. 

Hausmannite,  322. 
Heat  of  combustion,  152. 
Heavy  spar,  BaSO4,  89,  270. 
Helium,  245. 
Hematite,  307. 
Hemoglobin,  337. 
Holmium,  306. 
Homologous  bodies,  181. 
Horn  silver,  261. 
Hydrates,  51,  246. 

of  carbon,  220. 
Hydrazine,  N2H*,  100. 
Hydrocarbons,  01121+2,  178. 

nomenclature  of,  180,  183. 

unsaturated,  183. 

CnH2n,  185. 
Hydrogen,  16. 

absorption     by    palladium,     22, 
334. 

antimonide,  SbH3,  136. 

arsenide,  AsH3,  132. 


Hydrogen,  conductivity  for  heat,  21. 

diffusion  of,  19. 

dioxide,  55. 

phosphide,  PH3,  122. 

sulphide,  H2S,  75. 
analysis  of,  77. 
as  reagent,  77. 
Hydroxide,  51,  246. 
Hydroxyl,  65. 
Hypochlorites,  66. 
Hypochlorous  oxide,  C120,  65. 

Iceland  spar,  160. 
Illuminating  gas,  145. 
Indigo,  C16H10N202,  235. 

white,  C16H'2:N202,  236. 
Indium,  300. 
Ink,  233. 

sympathetic,  320. 
Iodides,  248. 
Iodine,  69. 

test  for,  71. 
lodoform,  CHI*,  206. 
Iridium,  334. 
Iron,  307. 

blast-furnace  process,  308. 

bloom,  310. 

carbonate,  FeCO3,  160. 

cast,  311. 

Catalan  process,  307. 

chlorides,  316. 

galvanized,  281. 

gray,  311. 

oxides,  316,  317. 

passive,  316. 

pig,  310. 

pyrites,  74,  307,  318. 

soft,  315. 

sulphates,  90,  318. 

sulphides,  317. 

tests  for,  318. 

white,  311. 

Isomerism,  172,  186,  197,  345. 
Isometric  system,  242. 
Isomorphism,  90,  343. 


356 


INDEX. 


Jet,  147. 

Kaolin,  305. 
Kerosene,  182. 
Ketoses,  222. 
Kieserite,  277. 
Kupfernickel,  320. 

Labradorite,  305. 

Lactose,  CPH»0U,  223. 

Lamp-black,  148. 

Lanthanum,  306. 

Laughing-gas,  NJ0,  104. 

Law  of  Avogadro  and  Ampere,  39. 

of  definite  proportions,  36. 

of  Gay-Lussac,  36,  38. 
Lead,  272. 

acetate,  Pb(C2H802)2,  210. 

carbonate,  PbCO3,  160. 

chloride,  PbCl»,  274. 

chromate,  PbCrO*,  327. 

cupellation  of,  259. 

dioxide,  PbO2,  275. 

iodide,  Pbl2,  274. 

monoxide,  PbO,  275. 

nitrate,  Pb(N08)»,  118. 

poisoning  by,  274. 

red  oxide,  Pb304,  275. 

sulphate,  PbSO*,  91. 

sulphide,  PbS,  276. 

tests  for,  276. 
Legumine,  336. 
Lepidolite,  250. 
Levulose,  CWOe,  221. 
Life,  chemistry  of,  334. 
Lignite,  147. 
Lime,  CaO,  266. 

chlorinated,  CaCl(ClO),  66,  268. 
Limestone,  160. 
Limonite,  307. 
Litharge,  275. 
Lithium,  250. 
Lixiviation,  159. 
Lunar  caustic,  118. 

Magenta,  230. 


Magnesia,  MgO,  278. 

alba,  160. 

Magnesite,  160,  277. 
Magnesium,  277. 

ammonium  phosphate,  278. 
carbonate,  MgCO3,  160. 
chloride,  MgCl2,  277. 
citrate,  220. 

hydroxide,  Mg(OH)2,  278. 
oxide,  MgO,  278. 
sulphate,  MgSO4,  90. 
tests  for,  278. 
Magnetite,  307. 
Malachite,  289. 
Malt,  193. 

Maltose,  C6Hi206,  196,  224. 
Manganese,  322. 

dioxide,  MnO2,  322. 
oxides,  322. 
sulphide,  MnS,  324. 
tests  for,  324. 
Marble,  160. 
Marcasite,  318. 
Marl,  305. 
Marsh  gas,  178. 
Marsh's  test  for  arsenic,  133. 
Massicot,  275. 
Matches,  121. 
Meadow-sweet  oil,  231. 
Menthol,  C10H200,  235. 
Mercuric  chloride,  HgCl2,  292. 
cyanide,  Hg(CN)2,  169. 
iodide,  Hgl2,  293. 
nitrate,  Hg(N03)2,  118. 
oxide,  HgO,  293. 
Mercurous  chloride,  Hg2Cl2,  292. 
iodide,  Hg2!2,  293. 
oxide,  Hg20,  293. 
Mercury,  290. 

atomicity  of,  291. 
chloride,  292. 
cyanide,  169. 
fulminate,  195. 
molecular  weight  of,  291. 
oxides,  293. 


INDEX. 


357 


Mercury,  sulphide,  294. 

tests  for,  294. 
Metallic  bromides,  248. 

carbonates,  156. 

carbonyls,  153. 

chlorides,  61,  248. 

hydrates,  52,  246. 

nitrates,  115,  116. 

oxides,  246. 

sulphates,  87. 
Metals,  15. 

general  properties  of,  241. 

natural  state  of,  242. 
Methane,  CH*,  175. 
Methylamine,  CH3.NH2,  229. 
Methylaniline,  CH3.C6H6N.  229. 
Methylbenzene,  CIRC* IP,  189. 
Methyl  chloride,  CH3C1,  204. 

cyanide,  CH3CN,  210. 

hydroxide,  CH'.OH,  192. 

iodide,  CH3I,  178. 

oxide,  (CH3)20,  201. 

salicylate,  CH3.C7fi503,  232. 
Mica,  305. 
Milk,  338. 
Mineral  waters,  49. 
Minium,  275. 
Mispickel,  128. 
Molecular  weights,  determination  of, 

40. 

Molecules,  11. 
Molybdenite,  328. 
Molybdenum,  328. 
Monazite,  306,  331. 
Monoclinic  system,  343. 
Monosaccharides,  221. 
Morphine,  C"H«N03,  329. 
Myosin,  337. 

Naphtha,  182. 
Naphthalene,  C™Il*,  189. 
Narcotine,  C22R23NO',  239. 
Native  metals,  242. 
Neodymium,  306. 
Nessler's  reagent,  293. 


Niccolite,  320. 
Nickel,  320. 

carbonyl,  Ni(CO)*,  153. 

chloride,  NiCl2,  322. 

oxides,  322. 

plating,  321. 

sulphate,  NiSO*,  322. 

tests  for,  322. 
Nicotine,  C^iT^N2,  238. 
Niobium,  136. 
Nitrates,  115,  116. 
Nitric  oxide,  NO,  106.  :' 
Nitrobenzene,  C^NO2,  228. 
Nitrogen,  91. 

atomicity  of,  110. 

bromide,  NBr3,  104. 

chloride,  NCI3,  104. 

dioxide,  NO,  106. 

group  of  elements,  136. 

iodide,  103. 

monoxide,  N20,  104. 

pentoxide,  N205,  110. 

peroxide,  NO2,  108. 

trioxide,  N203,  109. 
Nitroglycerin,  C3H5(N03)3,  200. 
Nitrosyl  chloride,  NOC1,  108. 
Nitrotoluenes,  C6H*(CH3)N02,  229. 
Nitrous  oxide,  N20,  104. 
Nomenclature  of  acids  and  salts,  66. 

of  chlorine  compounds,  61. 

of  oxygen  compounds,  50. 
Notation,  42. 

Oils,  essential,  189. 

fatty  and  drying,  214. 
Olein,  C3H5(C18H3302)3,  214. 
Opium,  239. 
Organic  compounds,  173. 

chemistry,  173. 
Orpiment,  As2S3,  130. 
Orthoclase,  305. 
Orthophosphates,  126. 
Orthorhombic  system,  243. 
Osmium,  334. 
Oxalates,  217. 


358 


INDEX. 


Oxides,  50,  246. 
Oxygen,  23. 

in  air,  92. 

manufacture  of,  323. 

properties  of,  26. 
Oxyhydrogen  blow-pipe,  29. 
Ozone,  53. 

Palladium,  333. 

Palmitine,  C3H5(C16JI3102)3,  213. 

Paraffin,  182. 

Paris  green,  133. 

Pepsin,  339. 

Petroleum,  181. 

Pewter,  274. 

Phenol,  C6H5.0H,  226. 

nitro-,  227. 

test  for,  227. 
Phosphorus,  119. 

amorphous,  121. 

chlorides,  123. 

oxides,  123. 

Phosphonium  salts,  123. 
Photography,  264. 
Physical  changes,  7. 
Pig  iron,  310. 
Pitchblende,  328. 
Plaster  of  Paris,  89. 
Platinum,  332. 

black,  333. 

chlorides,  333. 

sponge,  332. 
Plumbago,  144. 
Polymerism,  185. 
Polysaccharides,  226. 
Porter,  196. 
Potassium,  254. 

acid  carbonate,  KHCO3,  160. 

acid  tartrate,  KC^O*3,  219. 

alum,  304. 

antimony  1  tartrate,  219. 

bromide,  KBr,  256. 

carbonate,  K2C03,  159. 

chlorate,  KC103,  69. 

chloride,  KC1,  256. 


Potassium  chloroplatinate,  257,  333. 

chromate,  K2Cr04,  326. 

cyanate,  KOCN,  171. 

cyanide,  KCN,  168. 

dichromate,  K2Cr207,  326. 

ferricyanide,  170. 

ferrocyanide,  K4FeC6N6,  169. 

hydroxide,  KOH,  255. 

hypochlorite,  KC10,  66. 

iodide,  KI,  256. 

manganate,  K2MnO*,  323. 

nitrate,  KNO3,  116. 

oxide,  K20,  254. 

permanganate,  KMnO4,  324. 

picrate,  KO.C6H2(N02)3,  228. 

-sodium  tartrate,  219. 

sulphate,  K2S04,  89. 

sulphocyanate,  KNCS,  174. 

sulphydrate,  KSH,  78. 

tartrate,  K2C4H406,  219. 

tests  for,  256. 

thiocyanate,  174. 
Pottery,  305. 
Praseodymium,  306. 
Propane,  C3H8,  179. 
Propyl  alcohols,  C3H'.OH,  197. 
Propylene,  C3H6,  185,  186. 
Prussian  blue,  170. 
Ptyalin,  339. 
Purple  of  Cassius,  300. 
Pyrites,  copper,  284. 

iron,  318. 

Pyrogallol,  C6H3(OH)3,  232. 
Pyrolusite,  322. 
Pyroxylin,  225. 

Quartz,  140. 

Quinine,  C20H2*N202,  239. 
sulphate,  240. 

Radicals,  87. 

acid  and  basic,  103. 
hydrocarbon,  178. 

hydrates  of,  192. 

oxides  of,  201. 


INDEX. 


359 


Realgar,  As2S»,  130. 

Red  precipitate,  293. 

Roinsch's  test  for  arsenic,  131. 

Respiration,  32. 

Rhodium,  334. 

Rhuthenium,  334. 

Rochelle  salt,  KNaC*H*0«,  219. 

Rock  crystal,  140. 

Rosaniline,  C2°H2iN30,  229. 

Rubidium,  257. 

Ruby,  304. 

Rum,  197. 

Rust,  315,  317. 

Ruthenium,  334. 

Rutile,  330. 

Saccharose,  C12H22On,  224. 
Safety-lamp,  176. 
Saltpetre,  116. 
Salts,  65. 

ethereal,  211. 

neutral  and  acid,  88. 
Samarium,  306. 
Sand,  140. 
Saponifi  cation,  214. 
Sapphire,  304. 
Scandium,  306. 
Scheele's  green,  133. 
Sea-water,  253. 
Selenite,  89. 
Selenium,  87. 
Serpentine,  277. 
Shot,  129,  274. 
Siderite,  307. 

Siemens  regenerative  furnace,  279. 
Silica,  SiO2,  140. 
Silicon,  140. 

oxide,  SiO2,  140. 
Silver,  257. 

arsenate,  Ag8AsO*,  130,  133. 

arsenite,  Ag2HAs08,  132. 

assay,  262. 

chloride,  AgCl,  261. 

chromate,  Ag2CrO*,  262. 

cyanide,  AgCN,  168. 


Silver  iodide,  Agl,  262. 

nitrate,  AgNO3,  118. 

orthophosphate,  Ag3P04,  126. 

oxide,  Ag20,  261. 

sulphide,  Ag2S,  262. 

tests  for,  262. 
Silvering,  262. 
Slow  combustion,  31. 
Smalt,  320. 
Smaltite,  319. 
Smithsonite,  160,  278. 
Soap,  214. 

salt-water,  215. 
Soapstone,  277. 
Soda-water,  154. 
Sodium,  251. 

acetate,  NaC2H302,  210. 

acid  carbonate,  NaHCO3,  158. 

acid  sulphate,  NaHSO*,  88. 

alum,  304. 

borates,  137,  139. 

carbonate,  Na2C03,  157. 

chloride,  NaCl,  253. 

dioxide,  Na202,  253. 

hydroxide,  NaOH,  252. 

hypochlorite,  NaCIO,  66. 

hyposulphite,  Na2S203,  81. 

methylate,  NaCH30,  193. 

nitrate,  NaNO3,  116. 

oxide,  Na20,  253. 

phosphates,  126. 

potassium  tartrate,  219. 

sulphate,  Na2S04,  88. 

sulphite,  Na2S03,  80. 

tests  for,  254. 

tetraborate,  Na2B4Q7,  139. 

thiosulphate,  Na2S203,  81. 
Solder,  274. 
Soluble  glass,  142. 
Spathic  iron,  160,  307. 
Specific  heat,  249. 
Spectroscope,  244. 
Spectrum  analysis,  242. 
Speculum  metal,  287. 
Speiss,  320. 


360 


INDEX. 


Spiegeleisen,  311. 

Spinel,  247. 

Stannic  chloride,  SnCl4,  330. 

oxide,  SnO2,  330. 
Stannous  chloride,  SnCl1,  330. 

oxide,  SnO,  330. 
Starch,  (OWO*)",  223. 
Stearin,  C3H5(C18H3&02)3,  213. 

candles,  214. 
Steel,  311. 

Bessemer  process,  312. 

tempering,  313. 
Stereoisomerism,  348. 
Stereochemistry,  346. 
Stibnite,  134. 
Strontianite,  160,  269. 
Strontium,  269. 

carbonate,  SrCO3,  160. 

chloride,  SrCl2,  269. 

dioxide,  SrO2,  270. 

hydroxide,  Sr(OH)2,  270. 

monoxide,  SrO,  270. 

nitrate,  Sr(N03)2,  118. 

sulphate,  SrSO4,  89. 

sulphide,  SrS,  269. 

tests  for,  270. 

Strychnine,  C21H22N202,  240. 
Substance,  definition,  7. 
Sugar,  cane,  C12H220",  224. 

grape,  C^H^O6,  223. 

milk,  ClaH«0",  225. 

of  lead,  Pb(C2H302)»,  210. 
Sulphates,  87. 

test  for,  88. 
Sulphides,  73,  248. 

tests  for,  75. 
Sulphites,  80. 

Sulpho-urea,  CS(NH2)2,  175. 
Sulphur,  73. 

atomicity  of,  86. 

dimorphism  of,  75. 

dioxide,  SO2,  79. 

soft,  74. 

trioxide,  SO3,  81. 
Sulphuryl  chloride,  S02C12,  86. 


Sulphydrates,  78. 
Symbols,  42. 
Synthesis,  33. 

Tannin,  233. 

Tanning,  233. 

Tantalum,  136. 

Tartar-emetic,  K(SbO)C4H406,  219. 

Tartrates,  219. 

Tellurium,  87. 

Thallium,  300. 

Theine,  C8HK>N*02,  238. 

Theobrornine,  C'H8N402,  238. 

Thiosulphates,  81. 

Thorite,  331. 

Thorium,  331. 

Thulium,  306. 

Thymol,  C«>H"0,  234. 

Tin,  328. 

dichloride,  SnCl2,  329. 

oxides,  330. 

sulphides,  330. 

tests  for,  331. 

tetrachloride,  SnCl4,  330. 
Titanium,  331. 
Toluene,  C6H5.CH*,  189. 
Topaz,  304. 

Trichloraldehyde,  C2C13HO,  207. 
Triclinic  system,  344. 
Trimethylamine,  (CH3)3N,  229. 
Trinitrophenol,  C6H2(N02)3OH,  227. 
Triphylite,  250. 
Tungsten,  328. 
Turnbull's  blue,  171. 
Turpentine,  C10Hi6,  189. 
Type-metal,  135. 

Ultramarine,  306. 
Uranium,  328. 
Urea,  CO(NH2)2,  172. 

molecular  structure  of,  173. 

nitrate,  CO(NH2)2HN03,  174. 

Vanadium,  136. 
Vegetable  parchment,  226. 


INDEX 


361 


Verdigris,  210,  286. 
Vermilion,  294. 
Vinegar,  209. 
Vitriol,  blue,  CuSO*,  90. 

green,  FeSO*,  90. 

oil  of,  H2SO*,  83. 

white,  ZnSO4,  90. 

Water,  32. 

electrolysis  of,  33. 

hard,  48. 

in  air,  94. 

mineral,  49. 

natural,  48. 

of  crystallization,  47. 

properties  of,  45,  47. 

synthesis  of,  34. 
Water-gas,  153. 
Whiskey,  196. 
White  indigo,  236. 
White  lead,  160. 
White  vitriol,  ZnSO*,  90. 


Wine,  196. 
Wintergreen  oil,  232. 
Witherite,  160,  270. 
Wolfram,  328. 
Wood-spirit,  192. 
Wrought-iron,  310. 

Yeast,  194. 
Ytterbium,  306. 
Yttrium,  306. 

Zinc,  278. 

carbonate,  ZnCO3,  160. 

chloride,  ZnCl*,  281. 

ferrocyanide,  Zn2(FeC6N<5),  282. 

oxide,  ZnO,  282. 

sulphate,  ZnSO,  90. 

sulphide,  ZnS,  282. 

tests  for,  282. 

white,  ZnO,  282. 
Zircon,  331. 
Zirconium,  331. 


THE   END. 


I 7C67 


THE  UNIVERSITY  OF  CALIFORNIA  LIBRARY 


